ASMS 1981

ASMS Nomenclature Committee Workshops

Minneapolis, 1981 [1]

Two workshops were held on Monday, May 25, 1981 and Thursday, May 28, 1981. 84 members attended the first Workshop and 35 members the second. A cqpy of the list of terms and definitions for use in mass-spectrometry that had.been prepared following last year's Workshop was distributed to each attendee. The list had already been circulated in advance to 50 people who had attended last year's Workshop or who had written request.ing that the list-be sent to them and their suggested modifications had been incorporated.

Each term on the list was considered in detail. A copy of the terms finally approved at the Workshops is attached.

Help was sought to prepare an additional list of terms for consideration at next year's Workshops. The following people volunteered to provide terms under the headings listed alongside their names

M.S. Story, Finnegan Instruments (Instrumentation detectors)

C.R. Lagergren, Battelle (Surface ionization thermal ionization)

M. Elliott, V.G. Ltd. [Isotope mass spectrometry)

F.A. Elder, Xerox Corporation (Knudsen cell mass spectrometry)

C.M: Judson, University of Kansas (Sample introdution)

Several other people offered to send additional terms (with or without definitions) for inclusion in next year's list.

(The deadline _for receiptOf terms by me is August 31, 1981. This will allow time for circulation of a new list of terms to the.attendees at this year's Workshops so that their com.e..s can be inclllded, and prepara.ion of an agreed list :for discussion at the 1982 Meeting in Hawaii).

The following decisions were taken unanimously:

l. That the.attached list of terms be submitted to the ASMS Board of Directors for theii-approval, with th.e fol lowi.g reconimcndations

(i) That if the1ist is approved, it _be considered 'provisional' for one more ye.r so as to _give all members a final-opportunity of commenting upon it.

(ii) That all comments received before December 31, 1981 be considered-bythe Chairman of the Nomenclature Committee who would then reco1t1mend to the Hoard, in the light of such comments, which terrnsshould be

issued as ASMS recommended terms.

{iii)_ That terms issued under the headings 'Vacuum' and 'Data System' should be separated into an Appendix to the list of recommended terms.

(iv) That the generosity of the American Vacuum Society in providing most of the terms under the heading 'Vacuum' should be acknolwcdged in the list.

2. That the same procedure as was used this year should be fol_lowcd again so that a further list of terms can be submitted to the Board in a year's time.e

J .H. Beynon

Chairman

Royal Socieiiy Research Unit

University College of Swansea

Singleton Park, SWANSEA SA2 SPP, UK

IONIZATION NOMENCLATURE

Electron Ionization This is the tenn used to describe ionization of any species by . electrons. The process may, fo_r example, be written M + e + M+ + 2e.for atoms or molecules, .. and M + e-. M+ + ze-for radicals.

Photo-Ionization This is the tenn generally used to describe ionization of any species by photons. Th_e process _may, _ for example, be written [Note: Electrons and photons do not ".impact" molecules or atoms. They interact with

them in ways that result in various electroriic excitations including ionization. For this reason it is recommended that the tenns 'Electron impact' and 'Photon impact' be not used]. Field Ionization This term relates to the removal of electrons from any species by interaction with a high electrical field.

Field Desorption This tenn is used to describe the fonnation of ions in the gas phase from a material deposited ona solid surface (known as an 'emitter') in the presenceof a high electrical field. 'Field desorption' is an ambiguous term because it implies that the electric field desorbs a material as an ion from some kind of emitter on which the materialis deposited. There is growing evidence that some of the ions fanned are due to thennal ionization, some to field ionization of vapor evaporated from material on the emitter. Because there is little or no ionization unless the emitter is heated by an electric current, 'field desorption' is a misnomer. The tenn is however firmly implanted in the literature and most users (by no means all) understand what is going on regardless of the implications of the term. In addition, no better simple tenn has been suggested to take itsplaceand so; reluctantly, it is recommended

that it be retained.. Chemi-ionization and chemical ionization are two tenns which sh.uld not be used inter-changeably.

Chemicionization refers to a process whereby gaseous molecules are ionized when theyinteract with other internally excited gaseous molecules or molecular moieties. Chemical ionization concerns the process whereby riew ionized speci_es are formed when gaseous molecules interact with ions. The process may involve transfer of an electron, proton or other charged species to or between the reactants. When a positive ion

results from chemical ionization, the tenn may be used without qualification. When a negative ion results, the term negative ion chemical ionization should be used.

Surface Ionization. takes place when an atom or molecule is ionized when it interacts with a solid surface. Ionization only.occurs when the work function of the surface, the temperature of the surface, and the ionization energy of the atom or molecule nave an appropriate relationship. Thennal Ionization takes place when an atom or molecule interacts with a heated surface or is in a gaseous environment at high_ temperatures.: [Examples of the latter may be a capillary a_rc plasma, a microwave plasma, or an inductively coupled plasma].

Atmospheric Pressure Ionization is an ambiguous term. In essence, it is used to describe chemical ionization at atmospheric pressure.. It is recommended that use of the term should be discouraged. Spark (Source) Ioniiation occurs when a_solid sample is vaporized and partially ionized by an intennittent electric discharge. Further ionization occurs in the discharge when gaseous atoms and small molecular moieties interact with energetic electrons in the intennittent discharge. It is recommended that the word 'source' be dropped from this te nn. 798

Auto-ionization occurs when an internally supra excited atom or molecular moiety loses an electron spontaneously without further interaction with an energy source. (The state of the atom or molecular_ moiety is known as a pre-ionization state). Associative Ionization occurs when two excited gaseous atoms or molecular moieties interact and the sum of their internal energies is sufficient to produce a single, additive ionic _nproduct.

Multi-photon Ionization occurswhen an atom or molecule and their concomitant ions have energy states whereby the energy in two or more photons can be absorbed. Penning Ionization occurs through the interaction of two or more neutral gaseous species at least one of which is internally excited. Charge Exchange (Charge Transfer) Ionization occurs when an ion/atom or ionn/molecule reaction takes place in which the charge on the ion is transferred to the neutral species without any dissociation of either. Ion-Pair Formation involves an ionization process in which a positive fragment ion and a negative fragment ion are the only products. Ionization Cross Section This is a measure of the probability that a given ionization process will occur when an atom or molecule interacts with an electron or a photon. Electron Attachment A resonance process whereby an external electron is incorporated into an atomic or molecular orbital of an atom or molecule. Ionization Energy This is the minimum energy of-excitation of an atom, molecule or molecular moiety required to remove an el.ctron in order to produce a positive ion. Vertical Ionization This is a prOce.s whereby an electron is removed from a molecule in its ground_or an excited state so rapidly that a positive ion is produced without change in the positio.s or momenta of the atoms. The resultant .on is often in an excited state. Adiabatic Ionization A process whereby an electron is removed from the ground state of an atom or molecule producing an ion in its ground state. Ionization A process which produces an ion from a neutral atom or molecule. Dissociative Ionization Im ionization process in which a gaseous molecule decomposes to form products, one of which is an ion.

Ionic Dissociation A decomposition of an ion into another ion of lower formula-weight and one or more neutral species. Ionization Efficiency is the ratio of the number of ions formed to the number of electrons or photons used. An Ionization Efficiency Curve shows the number of ions produced as a function of the energy of the electrons or photons used to_produce ionization. Laser Ionization occurs when a sample is irradiated with a laser beam. In the irradiation of gaseous samples, ionization occurs via a single-or multi-photon process. In the case of solid samples, ionization occurs via_ a thermal process. TYPES OF -IONS Positive Ion This is an atom, radical, molecule or molecular moiety which has lost one or more electrons thereby retaining an electrically positive charge. The use-of the term cation as an alternative is not recommended. The use of mass ion is not recommended. Negative Ion An atom, radical,molecule or molecular moiety in the vapor phase which has gained one or more electrons thereby acquiring an electrically negative charge. The use of the term anion as an alternative is not recommended. 799

Singly-, Doubly-, Triply-etc. Charged Ion These terms are used to describe an atom, molecule or molecular moiety which has gained or lost one, two, three or more electrons. The term multiply-charged ion is used to refer to ions that have gained or lost more than one electron where the number of electrons lost or gained is not designated. Parent Ion An electrically charged molecular moiety which may dissociate to form fragment. one or more of which may be electrically charged, and one or more neutral species. A parent ion may be a molecular ion or an electrically charged fragment of a molecular ion. Fragment Ion An electrically charged dissociation product of an ionic fragmentation. Such an ion may dissociate further to form other electrically charged molecular or atomic moieties of successively lower formula weight. (See also Daughter lon). Daughter Ion An electrically charged product of reaction of a particular parent ion. In general such ions have a dfrect relationship to a particular precursor ion and indeed may relate to a unique state of the precursor ion. nnThe reaction need not necessarilyinvolve fragmentation. ft could, for example involve a change in the number of chargescarried. Thus, all fragment ions are daughter ions but not all daughter ions are necessarilY fragment ions. Rearrangement Ion An electrically charged dissociation product, involving a molecular or parent ion, in which atoms or groups of atoms have transferred from one portion of a molecule or molecular moiety to another during the fragmentation process. Stable Ion An ion which is not sufficiently excited to dissociate into a daughter ion and associated neutral fragment(s) or to react further in any other way. Unstable Ion An ion which is sufficiently excited to dissociate within the ion source. Metastable Ion An ion which is sufficiently excited to dissociate into a particulardaughter ion and neutral species during the flight from the ion source to the detector. The dissociation is most readily observed when it takes place in one of the field-free regions in a mass spectrometer. Precursor Ion This term is synonymous with Parent Ion.

Product Ion This term is synonymous with .hter Ion. Molecular Ion An ion formed by the removal (positive ions) or addition (negative ions) of one or more electrons from a molecule without fragmentation of the molecular structure. The mass of lhis ion corresponds to the sum of the masses of the most abundant naturallyoccurring isetopes of the various atoms that make up the molecule (with a correction for the masses of the electrons lost or gained). For example, the mass of the molecular ion of ethyl bromide, C2H5Br will be 2xl2 plus Sxl.0078246 plus 78.n91839 minus the mass of the electron (me)-This is equal to 107.95751 u -mn, u being the unit of atomic mass based on the standard that the mass of the isotope 12c = 12u exactly. Isotopic Molecular.Ion A molecular ion containing one or more of the less abundant naturally occurring isotopes of the atoms that make up the molecular structure. Thus, for ethyl bromide there exist molecular isotope ions such as 13CCH5Br+ , C2H4D Br+ C2Hsn81Br+ , 13C2H581Br+ etc. , Isotopic Ion Any ion containing one or more of the less abundant naturallynoccurring isotopes of the elements that make up its structure. Isotopically Enriched Ions When the abundance of a particular isotope is increased above the level at which it occurs in nature and is incorporated in a molecule the term "isotopically enriched ion" is used to describe any ion containing the enriched isotope.

Dimeric Ion An ion formed either when a chemical species exists in the vapor phase as a dimer and can be detected as such, or when a molecular ion can attach to a neutral molecule within the ion source to form an ion such as [2M]n+ . where M represents the molecule.

Protonated Molecule An ion formed by interaction of a molecule with a proton abstracted from an ion, as often occurs in Chemical Ionization according to the reaction : M + XH+ + MH+ + X. The symbolism [M+H] + may al'so be used to represent the protonatedmolecule.

[Note : The wfdely-used term 'protonated molecular ion' to "describe the MH+ ion is not recommended. It suggests an association product of a proton with a molecularion]-..

Adduct Ion An ion formed by interaction of two species, usually an ion and a molecule, and often within the ion source, to form an ion containing all the constituent atoms of one species as well as an additional atom or atoms. Cluster Ion An ion formed by the combination of two or more molecules of a chemical

species often in association with a se_cond species. For example, [ (H2OlnHJ + is a cluster ion. 

Radical Ion An ion containing an un-paired electron which is thus both an ion and a free radical. The presence of the odd electron is denoted by placing a dot alongside the symbol for the charge. Thus, CzHG+ and SFG- are radical ions. Odd-electron Ion This term is synonymous .with Radical Ion. Even-electron Ion An ion containing nonun-paired electrons, for example CH3 in its ground state. OTHER TERMS

Mass Analygis A process by which a mixture of ionic or neutral species is identified according to the mass-to-charge (m/z) ratios (ions) or their aggregate atomic masses (neutrals) .. The analysis may be qualitative and/or quantitative. Detection of Ions In mass spectrometry this concerns the observation of the arrival of particular ionic species, at a detector under conditions that preclude orminimize ambiguities due to interferences. Ions may be detected by photographic or suitable

electrical me8.ns. 

Scanning Method This term refers to the sequence of control over operating parameters of a mass spectrometer which results in a spectrum of masses, velocities, momenta or energies. Sample Introduction This refers to the manner in which a material which is to be subject to analysis is placed in the ion source of a mass spectrometer before and/or during such an analysis. Vacuum System Those components used to lower the pressure within a mass spectrometer are all parts of the vacuum system. This includes not only the various pumping componentsbut also valves, gauges and associated electronic or other control devices, the chamber in which ions are formed and detected and the vacuum envelope. Data System The components used to record and process information during the analysis of a sample are part of the data system. This includes electronic or other control devices, and recording storage and data manipulation devices. Data Processing Once information is obtained with an appropriate data system, the information must be interpreted appropriate to the end use. Those steps which lead to this end use are of concern in data processing. Note that data processing does not necessarily include application of modern computer techniques. Data Reduction The process of transforming the initial digital representation of a spectrometer output into a form which isn.amenable to interpretation; for example, a bar graph or a table of ion currents.

This abbreviation is used to denote the dimensionless quantity formed by dividing the mass number of an ion by the number of charges carried by the ion. It. has long been called the mass-to-charge ratio although mis not the ionic mass nor is z a multiple of the electronic charge, e-. The abbreviation m/e is, therefore, not recommended. Thus, for example, for the ion C7H.+ , m/z = 45.5.

IONn/MOLECULE REACTIONS

Ion/Neutral Reaction A process wherein a charged species interacts with a neutral reactant to produce either chemically different species or changes in the internal energy of one or both of the reactants. (NB.. The term ion/neutral reaction is not ideal, simply because the word neutral is not

a noun. However, any alternatives such as ion/neutral-species a'.re so clumSy as to seem _ unlikely to be generally accepted). Ion/Molecule Reaction An ion/neutral reaction in which the neutral species is a molecule. Charge Inversion Reaction An ion/neutral reaction wherein the charge on the reactant ion is reversed in sign. Charge Transfer Reaction An ion/neutral reaction wherein the total charge on the reactant ion is transferred initially to the reactant neutral species so that thereactant ion becomes a neutral entity. Partial Charge Transfer Reaction An ionn/neutral species reaction wherein the chargenon a multiply-charged reactant ion is reduced. Charge Stripping Reaction An ion/neutral reaction wherein the charge on the reactant ion .n is made more positive. Charge Permutation Reaction This is a general term to describe an ion/neutral reaction wherein there is a change in the magnitude.nand/or sign of the charges on the reactants. (Note : Considering some of t.he possible reactions of ions M2+ , M+ and W with a neutral species N these would be categorised on the basis of the above definitions as follows M+ M2+ + N -+ + N (Partial charge transfer)w + N -+ M2++ N + e (Charge stripping) M+ . w + N -+ + N + 2e (Charge stripping and charge inversion) .nAll are ion/neutral reactions and also charge permutation reactions]. Collision-induced Dissociation An ion/neutral process wherein the (fast) projectile ion is dissociated as a result of interaction with a target neutral species. This is brought about by conversion of part of the translational energy of the ion to internal energy in the ion during the collision. Collisional Activation An ionn/neutral process wherein excitation of a (fast) projectile ion is brought about by the same mechanism as in collision-induced dissociation. (The ion may decompose subsequently)n. Collisional Excitation An ion/neutral process wherein ther<; is an increase in the (slow) reactant ion's internal energy at the expense of the translational energy of either (or both) of the reacting species. The scattering angle may be large. (Note : It is recommended that all three of the above terms should be retain.ed]n. Elastic Scattering An ion/neutral interaction wherein the direction of motion of the ion n is changed, but there is no change in the total translational energy or internal energyof the collision partners. Inelastic Scattering An ionn/neutral interaction wherein the direction of motion of the ion is changed, and the total translational energy of the collision partners is reduced.

Elastic Collision A collision resulting in elas_tic scattering. Inelastic Collision A collision resulting in inelastic scattering. Superelastic Collision A collision in which the translational energy of the fast-movingcollision partner is increased. Ionizing Collision An ion/neutral reaction in which an electron or electrons are strippedfrom the ion and/or the neutral species in the colli_sion. 'Generally, this term has come to be used to describe collisions cif fast moving ions with a neutral species in which the neutral species is ionized with no change in .the number of charges carried by the ion. Care should be taken when this term is used to emphasize if charge stripping of the ion has taken place. Assocfation Reaction (associative combination) The reaction of a (slow moving) ion with a neutral species wherein the reactants combine to form a single ionized species. Ion/neutral Exchange Reaction In this reaction an Association Reaction is accompanied bythe subsequent or simultaneous liberation of a different neutral species as product. Translational Spectroscopy A technique to investigate the distribution of the velocity of product ions from ion/neutral reactions. Ion Energy Loss Spectra Spectra that show the loss of translational energy of ions involved in ion/neutral reactions.

Impact Parameter The distance'of closest approach of two particles if they had continued in their original direction of motion at their original speeds. Interaction Distance The furthest distance of approach of two particles at which it is discernible that they will not pass at the impact parameter. Charge Exchange Reaction This term is synonymous with Charge Transfer Reaction. Partial Charge Exchange Reaction This term is synonymous with Partial Charge Transfer Reaction. SCANNING OF SPECTRA Mass Spectrum A spectrum obtained when a beam of ions is separated according to the mass.to-charge (m/Z) ratios of the ionic species contained within it. [Note : A quadrupole mass spectrometer achieves separation of the various ionic speciesin this way].

Momentum Spectrum A spectrum _obtained when a beam of ions is separated according to the momentum-to-charge rati.os of the ionic species contained within it. [Note : A sector magnetic field achieves separation of the various ionic species in this way. If the ion beam is homogeneous in translational energy, as is the case with sector instruments, separation according to the m/z ratios is also achieved].

Ion Kinetic Energy Spectrum A spectrum obtained when a beam of ions is separated according to the translational energy-to-charge ratios of the ionic species contained within it. [Note : A radial electric field achieves separation of the various ionic species in this way].

Magnetic Field Scan The usual method of producing a momentum (mass) spectrum in instruments. Accelerating Voltage (High Voltage) Scan An alternative method of producing a momentum (mass) spectrum in magnetic deflection instruments. This scan canna1so be used, in conjunction with a fixed radial electric field to produce an ion kinetic energy spectrum.

Linked Scan A scan, l'.n an" instrument comprising two or more analysers, in which two or more of the analyser fields are scanned simultaneously so as to preserve a pre.determined relationship between parameters characterising these fields. often, these parameters are the field strengths, but may also be the frequencies in the case of analysers in which alternating fields are employed_ ..

Linked Scan at Constant B/E A linked scan at constant B/E may be .erformed on a sector instrument.incorporating at least one magnetic sector plus one electric sector. It involves scanning the magnetic sector field-strength B and the electric s_ector field.strength E .simultaneously, holding the accelerating voltage V constant, so as to maintain the ratio B/E at a constant value. This constant value is determined bythe ratio of the two field strengths which transmit main-beam ions of predete.rminedmass:charge ratio; these preselected main-beam ions are the precursor ions whose fragment-ion spectrum is required. The fragmentation reactions so observed occur in a field-free region traversed before the two sectors scanned in this way. [Notes: This terT!I should not be used without prior explanation of the meanings of B and E. The term "B/E linked scan" is not recommended. It may suggest that the ratio B/E varies during the scan]. Linked Scan at Constant E2 /V A linked scan at constant E2 /V may be performed on a sector instrument incorporating at least one electric sector plus one magnetic sector. It involves scanning the electric sector field E and the accelerating voltage V simultan.eously, so as to ,naintain the ratio E2/V at a constant value, equal to the value of this ratio which transmits the main beam of ions through the electric sector. The magnetic sector field is set at a fixed value such. that main-beam ions of a pre.determined mass:charge ratio are transmitted by the magnet; these preselected main.beam ions are the precursor ions whose fragment-ion spectrum is required. The fragmentation reactions so observed occur in a field-free region traversed before the two sectors scanned in this way. [Notes : This terT!I should not be used without prior explanation of the meanings of E and V. The term "E2 /v linked scan" is not recommended],

Linked Scan at Constant B2 /V A linked scan at constant B2 /E may be performed on a sector instrument incorporating at least one electric sector plus one magnetic sector. It involves holding the accelerating voltage fixed, and scanning the magnetic field Band the electric field E simultaneously so as to maintain the ratio 82 /E at a constant value. This constant value corresponds to the ratio of the two fields which 'transmit main-beam ions of predetermined mass:charge ratio; these preselected main-beam ions are the fragment ions whose precursor-ion spectrum is required. The fragmentationreactions thus observed occur in a field-free region traversed before the two sectors scanned in this way.

[Notes : This term should not be used without prior explanation of the meanings of Band E. The term "B2 /Elinked scan" is not recommended] . 1 Linked Scan at Constant B l[ (E/E0)]l /E A 1 inked scan at constant B[l -(Ee/E0)]'/E may be performed on a sector instrument incorporating at least one electric sector plus one magnetic sector. It involves holding the accelerating voltage fixed, and scanning the magnetic field Band electric field E simultaneously, so as to maintain the quantityB[l -(E/Eo)]l/E at a constant value. This constant value is equal to B3/E0 , where E0 and B3 are respectively the electric sector field and magnetic sector field required to transmit m; ions in the main ion-beam; me3 represents the mass (m1 -m2) of the selected neutral fragment whose precursor ion spectrum is required. The fragmentationreactions so observed occur in a field-free regio. traversed before the two sectors scanned in this way.

[Noten: This term should not be used without prior explanation of the meanings of B, E and E0 .

The term "B [l -(E/E0)] '/E linked scan" is not recommended]. The above three definitions are merely examples of the types of linked scan that might be used. Any other linked scans can readily be defined inna similar manner.

Fixed Precursor Ion Scans 1. Mass Selection followed by Ion .Kinetic Energy Analysis If a precursor (parent) ion is selected, for example by a magnetic sector, all product ions formed from it in the field-free region between the magnetic sector and a following electric sector can be identified by scanning an ion kinetic energy spectrum. 2. Linked Scan at Constant B/E or at Constant E2 /V Both of these linked scans give a spectrum of all product (daughter) ions formed from a preselected precursor (parent) ion.

Fixed Product-Ion Scans 1. High Voltage Scan.

2. Linked Scan at Constant B2 /E.

Both 1. and 2. give. a spectrum of all precursor (parent) ions that fragment to yield a pre-selected product (daughter) ion.

Fixed Neutral Fragment Scans 1 The linked scan at constant B[l -(E.'E0)]'/E gives a spectrum of all product (daughter)ions that have been formed by loss of a pre-selected neutralfcagment from any precursor(parent) ions. [Note : The above definitions. have all been given with reference to sector instruments; linked scans to give similar information have also been devised for instruments incorporating one or more quadrupoles].

2E Mass Spectrum Processes of the partial charge-transfer type 2+ + N+

m + N . m + occurring in a collision cell (containing a gas, N) located in a field-free region preceding a magnetic and electric sector combination placed in either order, may be . detected as follows. If the instrument slits are wide, and if the electric sector field Eis set to twice the value required to transmit the main ion-beam, the only ions to be trans.mitted will be those with a kinetic energy/charge ratio twice, or almost exactlytwice, that of the main ion-beam. The product ions of the process shown fulfill this condition. If the magnetic field Bis scanned, a mass spectrum of such singly.charged product ions, and thus of their doubly-charged precursors, is obtained. Such a spectrum is called a 2E mass spectrum.

E/2 Mass Spectrum Processes of the charge-stripping type

m+ + N . m2+ + N + e- occurring in a collision cell (containing a gas N) located in a field-free regionpreceding a magnetic and electric sector combination placed in either order, may be detected as follows. If the instrument slits are wide and if the electric sector field Eis set to half the value required to transmit the main ion-beam, the only ions to be transmitted will be those with a kinetic energy/charge ratio half, or almost exactly half, that of the main ion-beam. The product ions of the charge-stripping process fulfill this condition. If the magnetic field Bis scanned, a mass spectrum of such doubly-charged product ions, and thus of their singly-charged precursors, is obtained. Such a spectrum is called an E/2 mass spectrum.

. [Note Interference from product ions from processes of _the type +

m1 + -m2) where m2 . 0.5 m1, can arise in E/2 mass spectra]. Charge Inversion Mass Spectrum Charge inversion processes of the types or m-+ N . m+ + N + 2e. respectively, occurring in a collision cell (containing a gas, N) located in a field.fr_ee region preceding a magnetic and electric sector combination placed in either order, may be detected as followsn. If the instrument slits are wide, and if the connections to the two sectors, appropriate to transmission of either positive or negative main-beam ionS, are simply reversed, the negative or positive product ions of the two processes,respectively, will be transmitted. If the magnetic field is scanned, a spectrumof such product ions will be obtained, and this spectrum is called a charge-inversion mass spectrum. These spectra are sometimes referred to as -E and +Enspectra, respectively. [Note : The terms "2E, E/2, -E or +E mass spectrum" should not be used without priorexplanation of the meaning of 2E, E, +E or -E]n.

APPENDIX

VACUUM

(The terms in this section have been contributed, almost entirely, by the American Vacuum Society, to whom grateful acknowledgment. is made)

Adsorption The process by which gas or vapor is bonded on a solid or liquid surface. Aperture lmpedance The additional resistance encountered by gas flowing through _a tube with an abrupt reduction in cross-section. For molecular flow, it. is the product . of the molecular effusion impedance of an orificenwith a cross-sectional area A2 and the aperture correction factor (l -A2/A1), whereO A1 is the cross-sectional area of the larger tube and A2 that of the smaller tube.

Background Spectrum A mass spectrum of residua! gas speciesin a system. It is usually obtained before a sample of interest is introduced and analyzed in 9rder to deduce by subtraction of spectra the true mass spectrum of the sample. Backstreaming The flow of charged and/or neutral particles emanating from a pump and moving counter to the flow of the gases being pumped. Baffle A series of surfaces placed in the line of gas or vapor flow to prevent straight------rTn e fl ow . Collision Frequency The number of molecules or atoms striking a unit area of surface per unit time; also, the number of.collisions between the molecules or atoms in a gas per unit volume and unit time. The collision frequency per molecule is equal to the probability per unit time that a molecule will collide with a surface or another molecule. Collision Rate The collision probability.per unit time for an atom or molecule travel-ling at a specified speed through a gas. Conductance The ratio of throughput, under steady-state conservative conditions, to the pressure differential between two specified cross-sections inside a pumping system. Critical lnlet Pressure The inlet pressure of a vapor pump above which an abruptdecrease in pumping speed occurs.

.

Cryopump A vacuum pump which operai:es by the condensation and/or sorption of gas at surfaces maintained at temperatures sufficiently low for the vapor.pressures of the condensed gases to be insignificaTit. Cryosorption Pump A vesse_l containing an adsorbent which can be refrigerated for the cryosorption pumping of gases. Cryosorption Pumping A technique of producing vacuum by physical adsorption o_f gases on solid adsorbents cooled t. low temperatures. _n

Diffusion Pump A vapor pump in which the pumped gas flows into a vapor stream under conditions in which molecular flow predominates. Momentum is transferred from the vapor to the gagJ, carrying it along in the direction of the stream:n Pump fluid is hea'ted in vacuum to generate the vapor which is directed through a nozzle. It expands freely in the stream before it reaches a cool wall where it condenses and is returned to the boiler to begin a new cycle.

Ejector Pump A vapor pump in which the pumped gas enters the pump and the v_apor stream under predominantly viscous flow conditions. Evaporation The conversion of a substance from the liquid state into the gaseous state by absorption of energy.

Exhaust Port An opening in a vacuum pump or stage from which gases are ejected either to a succeeding stage or to the atmosphere. Feedthrough A device for transmitting electrical current, fluids or mechanical motion through the wall of a vacuum system. Flange A (projecting) rim usually in the form of an annulus intended for fastening and sealingnone part of the vacuum system to another. .n Flapper Valve A thin gauge spring steel plate fastened on one end to the pump housing which seals the exhaust port of a mechanical pump from the oil r.servoir or atmos.phere. During the exhaust cycle, gas pressure is sufficient to deflect the plate away from its seat and gas is discharged from the pump. Syn: flutter reed valve. Flow (Gas) The motion or passage of a gas. A description of gas flow may be character.ized by the Knudsen number into three ranges. Molecular Flow The flow of gas through a channel und.r conditions such that the mean free path is much greater than the largest dimension of a transverse section of the channel. .nAt these pressures, the flow characteristics are determined by collisions of the gasmolecules with the channeTsurfaces and flow effects from molecular collisions are

insignificant. Transition Flow The flow of a gas through a channel under conditions that the mean free path is of the same order as the transverse dimensions of the channel. In this pres.sure range, the flow characteristics are determined by collisions of the gas molecules with surfaces as well as with other gas molecules. Also called Knudsen flow. Viscous Flow The flow of a gas through. a channel under conditions such that the mean free path is very small in comparison with smallest dimension of a transverse section of the channel. At these pressures the flow characteristics are determined mainly by colli.sions between the gas molecules, i.e. the viscosity of the gas. The flow may be lamlnar or turbulent. Fore Pump A vacuum pump for maintaining the forepressure of another pump below its critical value.

Forepress ure The pressure measured downstream from the outlet or foreline of a vacuum _ pump. Fractionating Pump A diffusion pump whose design allows the more vol a ti le impurities in the pump fluid resulting from decomposition or contamination to be either ejected out of the foreline or trapped within the pump in such a manner as to effectively reduce their chance of escape out of.the pump inlet. Holding Time (Pump) The time required for the forepressure of an isolated vapor or diffusion pump to reach the limiting forepressure. Hot Cathode Ionization Gauge An ionization gauge in which pressure is measured in terms of the current of positive ions produced by electrons emitted from a heated catllode. Bayard-Alpert Gauge A hot cathode ionization gauge in which a fine wire ion collector is positioned on the axis of a cylindrical grid functioning as anode. The cathode is mounted outside the grid. Impedance The reciprocal of .conductance. Incidence Rate The number of molecules striking a unit area of surface per unit time. Inlet Pressure The gas pressure at the entrance to a pump.

Interstage Pressure The gas pressure at any point between the exhaust port of the low-pressure stage and high-pressure or roughing stage of a compound .pump. Ion Pump An electron device in which ionization produces a significant rate of gasr.moval. Differential Sputter Pump A sputter-ion pump having two cathodes for which materials and sputtering rates differ. Diode Pump An ion pumpcontaining two uniquely shaped electrodes, viz. a cathode and anode. Two-electrode ion pumps are also referred to as diode getter and. diode sputter ion pumps. Electrostatic Pump An ion pump having only ele.ctrostatic fields rather than .both electric and magnetic fields to generate the ionizing discharge. The getter material is sublimed by electron heating or by ohmic heating into the discharge space. Electrostatic Getter Pump An electrostatic-ion pump in which a getter material is made to sublime. Evaporation Pump A getter-ion pump in which the getter is evaporated from a molten surface rather than sublimed or sputtered from a solid source. Getter Pump A pump which combines the pumping mechanisms used in the ion pump and the getter pump. (See sputter-ion pump and. electrostatic pump). Magnetic Pump An ion pump usually with multiple anode cells immersed in a magnetic field parallel to the cell axes with two cathode end plates of reactive material spaced from the ends of the anode cells. which terminates the discharge space. Noble Gas Pump A magnetic-ion pump with novel cathode geometries to enhance the pumping of noble gasese. Sputter Pump A getter-ion pump in which the getter surfaces are continuously renewed by sputtering. Triode Pump An ion pump usually of the sputter-ion type, containing three uniquelyshaped electrodes; an anode, a sputter cat.ode, and an ion collector electrode. Triode Getter Pump A triode-ion pump in which gettering is a part of the pumping mechanism. Knudsen Flow The flow of .gas through a pump or system under transition flow conditions which are ientermediate between visCOus flOw and molecular flow. Knudsen Gauge A vacuum gauge which indicates pressure by responding to the net rate of transfer of momentum by molecules moving between two surfaces maintained at different temperatures and separated by a distance smaller than the mean free pathof the gas molecules. Various types of Knudsen gauges differ mainly in the shapeand method of suspension of the movable element. Knudsen Number The ratio ofe.the mean free path of a gas molecule to a characteristic dimension of the channel through which gas is flowing. For a cylindrical tube, the diameter is a characteristic dimension. Leak A hole or permeable element through which leakage may occur under the action of a pressure difference. This includes a device used to introduce gas into a vacuum system at a controlled rate. Calibrated Leak A leak which has a known leakage rate for a specific gas under specific conditions.

Capillary Leak A leak having a smalel cross section dimension and lengtn many times its cross section dimension. Membrane Leak A leak which permits gas flow by permeation through a thin nonporous wall._ Molecular Leak A leak of such a size that the leakage through it is predominantlymolecular flow for a given pressuree, Variable Leak A leak with an adjustable leakage rate which can be controlled. Virtual Leak An apparent leak because of the presence of contaminants which outgas veryslowly within a.vacuum system. Viscous Leak A leak of such a size that the leakage through it is predominantly viscous flow for a given pressure. Accumulation Leak Detection Technique A leak detection technique in which tracer gas (e.g. helium) enters the part under test and is allowed to accumulate within the part, or within a system containing the part, for a period of time. The part or system is then opened to the leak detector. The system may include the leak detector sensingelement. Backing Space Leak Detection Technique A leak detection technique in which the leak detector is connected to the forevacuum side of a pump attached to the vacuum system A.e or element undergoing leak teste. tracer gas is sampled at a higher pressure after compression by the diffusion pump or other type of pump operating at high speed relative to its backing pump. Bagging A jargon term for a leak detection technique in which the part under test is enclosed in a bag (or other enclosure) which is filled with a tracer gase_to slightly more than atmospheric pressure. A tracer gas is applied to the entire. surface of the part to determine the total leakage from all leaks in the part. Diffusion Leakage A leakage resulting from the temperature dependent diffusion of a specific gas through a membrane. Examples are the diffusion of hydrogen through palladium and helium through glass. Leakage (leak) Rate The quantity of gas passing through a leak in a given time divided bythat time (see throughput). Limiting Forepressure The pressure at the discharge side of a vacuum pump, at a stated throughput, above which the pumping action of the pump rapidly deteriorates, evidenced by a sudden increase of inlet.pressure. Syn: critical backing pressure. Load (Vapor Pump) The quantity of gas, not including pump fluid vapore, in mass units, flowing through the pump per unit time. It is also called capacity or mass flow. Manometer An instrument for measuring the pressure of gases and vapors. Maximum Pressure Ratio (Vacuum Pump) The maximum value of the ratio ofe_forepressure to inlet pressure which a pump. can maintain at zero gas .-flow. In_ vapor pumps, this term is usually significant only for.light gases such as hydrogen and helium. McLeod Gauge A liquid level manometer in which a known volume of the gas, whose pressure is to be _measured, is compressed by the movement of a liquid column and confined in a small measurable volume. Corrections need to be made for any appreciable change in gas pressure in the system caused by the movement of the liquid. Mean Free Path The average distance a particle travels between successive collisions with the other particles of an ensemble.

Mean Path The mean distance a particle travels between successive collisions with other particles or surfaces. When the pressure is high or the vessel dimensions are large, so that the mean path is small with respect to the vessel dimensions, the mean path and mean free path become numerically identical. .n

Mechanical Pump (Vacuum) A device with moving parts such as r.tating vanes, a piston, or eccentric rotary members used for pumping gas or vapor.

M:>lecular Effusion The molecular flow of gas from a region at one pressure to one at a lower pressure through an orifice in a wall of negligible thickness and with a diameter much less than the mean free path of the molecules. Molecular Flux The net number of gas molecules crossing a specified surface in unit time. Those having a velocity component in the same direction as the normal to the surface at the point of crossing are counted as positive and those having a velocity component in the opposite'ndirection are counted as negative. Molecular Velocity Distribution The average value of the fraction of the molecules in a small volume, dr, surrounding a given point, located by the radius vector r in a fluid medium, which have velocity vectors lying within an infinitesimal volume, dv, surround.ing the point in velocity space. The averaging process is carried out over a time long enough to smooth statistical fluctuations in the molecular populations,.but short compared with the time required for significant variations in the macroscopic properties. For a gas in equilibrium at rest, the distribution of the velocity vectors with a givenmagnitude is uniform over a sphere about the origin in velocity space. The distribu.tion known as Maxwell's Jaw of velocity distribution is fv dv=4rrv2 (m/2rrkT)3/2 exp(-mv2/2kT)dv, where mis the mass of a molecule, Tis the absolute temperature,k is the Boltzmann constant, and 4rrv2 dv is the volume of a spherical shell of radius equal to the magnitude of v and of thickness dv equal to the increment in this magnitude and gives the fraction of molecules having speeds between v and V + dv. The function fv is the Maxwellian distribution function. Net Speed (Vacuum Pump) The throughput across a section remote from the pump inlet divided by the pressure as measured at that section. The net speed can be calculated when the pumping speed is known by adding to the sum of all the impedances between the pump inlet and the given cross section, the reciprocal of the measured pumping speed and then taking the reciprocal of the result. Pascal The basic S.nI. unit of pressure recommended for general use in vacuum technology. ---I-t-is one newton per square meter. (see also : Torr). Permeability Coefficient The rate of flow of gas through a unit area and a unit thickness of a solid barrier per unit differential pressure at a given temperature. Permeation The passage of gas through a solid. The process always involves diffusion through the sol id and may involve surface phenomena such as sorption, dissociation , migration and desorption. Physical Adsorption An adsorption process caused by .van der Waals forces .etween adsorbent and adsorbate. Typical binding energies are less than JO kcal/mole. Syn: physisorption. (See adsorption.) Positive Displacement Pump A mechanical vacuum pump in which the pumping action is provided by displacement or trapped volume of gases typically by a rotating or

reciprocating piston, sliding vane, or intermeshing lobes. _ Pressure (Gas) The average normal force per unit area exerted by gas molecules impacting on a surface.

Ultimate Pressure The limiting low pressure approached in a vacuum system after a sufficient pumping time has elapsed to establish that further reductions in pressure will be negligible. Sometimes called the ultimate vacuum, or blank-off pressure, or base pressure when referred to a pump under test.

Ultimate Partial Pressure The part of the ultimate pressure in a vacuum system caused by the partial pressure of a specific gas.

(Saturated) Vapor Pressure The pressure of a vapor in thermodynamic equilibrium with a condensed phase at a fixed temperature. The definition applies to single components as well as to multicomponent systems. In the latter case, it is necessary ton, distinguish between the total pressure over the condensed phase and the partial pressure of a given component. Syn : saturation pressure. Pump Fluid A liquid, usually having a low vapor pressure, used as the working fluid in a mechanical or vapor pump. Pumping Speed The ratio of the throughput of a given gas to the partial pressure of that gas at a specified point near the inlet.nport of a pump. Seal A joint between two elements of a vacuum system which is effective in maintaining leakage at or below a required level. A seal which can be baked at elevated temperatures.

Break Seal A seal consisting of a thin glass membrane separating adjacent sections of a The m.mbrane is broken to connect the _two sections. A seal between two elements designed for disassem.ly without resort to cutting, fracturing, or melting, which is effective in matntaining the desired vacuum.

Gasket Seal A demountable seal which employs a closed loop of deformable material pressedbetween two harder members. It may be reuseable. The gasket may be fabricated from metal washers, wire' rings, el3.stomers orn.other materials. 0-Ring A demountable, elastomer, gasket seal made with a toroidal gasket of circular cross section. Pump Speed The volumetric rate of gas flow across a section at the pump inlet. It can be obtained from the ratio of the throughput .nof a gas to the partial pressure of that gas at a specific point near the inlet port of the pump. (OHen called pumping speed.n)

Speed Factor The ratio of the speed to the product of the vacuum pump inlet cross section area and the maximum flow rate per unit area as given by the effusion law. It is also called efficiency, or speed efficiency. Speed of Exhaust The instantaneous rate of reduction of pressure in a systemnmultiplied .n by its volume and divided by its pressure. Sticking Coefficient The ratio of the number of molecules which are adsorbed on a surface for a finite period of time to the number of molecules striking that surface.

Sublimation The process of transition directly from the solid vapor phase without 0 passing through the intermediate liquid phase by the absorption of energy.Synn: sublime.

Thermal Conductivity Gauge A vacuum gauge containing two surfaces at different tempera.tures between which heat can be transported by gas molecules. Changes in the temperatures, or in the heating power required to maintain constant temperature of one of the surfaces can bencorrelated with the gas pressure. Thermal conductivity gauges differ in the method of indicating the temperature change. (See : thermocouple gauge).

Thermistor Gauge A form of thermal conductivity gauge in which the temperature.sensitive elements are made of semiconducting material instead of metal.

Thermocouple Gauge A thermal conductivity gauge which contains a heated filament and a thermocouple for the measurement of filament temperature as a function of gas pressure. Throat (Vacuum Component) (a) (Nozzle or Diffuser). The smallest cross section of an expanding nozzle, converging diffuser or converging/diverging nozzle or diffuser. (b) (Vapor Pump). The smallest clearance area between the pump casing and the nozzle nearest the inlet port.

Throughput The quantity of gas in pressure-volume units, at a specified temperature,flowing per unit time across a specifiednopen cross section. Throughput may be n referred to a specific constituent of a gas in which case the partial .pressure of that constituent and the associated flow rate are the relevant quantities.

Torr A unit of pressure defined as 1/760 of a standard atmosphere. It replaced the term .--millimeter of mercury (mm of Hg), and has now been replaced by the Pascal as a preferredunit of pressure. (1 mm Hgn= 1.000 000 14 Torrn= 133.322 386 7 Pas. Trap (Vacuum System) A device used in a vacuum pumping line to reduce vapor pressure in a vacuum system or prevent backstreaminng and migration of vacuum pump fluids such as mercury and/or oil. Anti-Migration Trap A trap which. includes a chilled surface or other means to preventn surface migration of oil from a source into the vacuum system.

Cold Trap A trap with a refrigerated surface used to condense various vapors present in the vacuum system. Molecular Sieve Trap A trap containing molecular sieve material that has a high surface area and that.nadsorbs hydrocarbon and water vapors at or below room .temperaturen.

U-Tube Trap A trap in the form of a U-shaped tube which is immersed in a coolant. Turbomolecular Pump An axial flow turbine for operation in the molecular flow rangeconsisting of a series of alternate circular rotor and stator disks both of which have inclined blades designed to impart momentum change to gas molecules in a preferential direction from the pump inlet to the outlet. Vacuum The condition of a gaseous environment in which the gas pressure is below .mospheric pressure. Low Vacuum A vacuum in which the pressure is less than 105 Pa (.750 Torr) and greaterthan 3.3 x 103 Pa (25 Torr). Medium Vacuum A vacuum in which the pressure is less than or equal to 3. 3 x 10n3 Pa (25 Torr) and greater than 10-1 Pa (7.5 x 10-4 Torr). High Vacuum A vacuum in which the pressure is less than or equal to 10-1 Pa (7.5 x 10-4 Torr) and greater than 10-4 Pa (7 .5 x 10-7 Torr).

Very High Vacuu!!!_ A vacuum in which the pressure is less than or equal to 1O-4nPa (7.5 x 10-7 Torr) and greater than 10-7 Pa (7.5 x 10-10 Torr).

Ultrahigh Vacuum A vacuum in which the pressure is less than or equal to 1O-7nPa (7.5 x 10 lo Torr) and more than 1O-1n Pa (7.5 x 10-13 Torr).

Extreme Ultrahigh Vacuum A vacuum in which the pressure is less than io-10 Pa (7.5 x 10-1n3 Torr). . '

Vacuum Valve A mechanical device by which the flow of. gas or vapor may be started, stopped, or regulated by a moving part which opens or obstructs a passage. Angle Valve A valve in which the ports are not in line, as, for example, a right angle valve.

Vacuum Baffle A vii.Ive containing a shield whic_h rem_ains in linne with thne valve port and can thus act as a baffle. Butterfly Valve A valve which is opened or closed by rotating a disk goo about an axis through the center of the disk. Diaphragm Valvne A valvne in which thne valve stem is mounted in a bonnet which is isolated from the rest of the valve by using a diaphragm to divide the space inside the valve body. Either metal, elastomer or plastic is commonly used for the diaphragm.An elastomer or plastic diaphragm sometimnes functions also as a gasknet. In any-case, motion is limited to avoid exceeding the elastic limit of the diaphragm material. Leak Valvne A valve for admitting air or gas at a precisely determined rate into a vacuum system.

Needle Valve A leak valve in which a tapered needle is moved along its axis against a seat which may also be tapnered. Relief Valve A valve which will automatically open when the pressure on the seat side It is gennerally regarded as a-safety device. A valvne usually for high vacuum applications, in which thne stem is One end of the bellows is attached to the valve body and the other end to the disk part of the valvne stem. A valve in which the movable member is actuated electrically by an A valve in which the ports are in line, or coaxial, and for which thne internal construction is such that line-of-sight flow occurs when thne valve is open.

!Hta Acquisition The process of transforming representations of (spectrometer) signals from their original form into suitable representations , with or without modification , in conj unction with a computer system .

Real Time In data acquisition in Real Time the computer representations are generated within the same time frame as the original experiment. Off-Line In this method of data acquisition there is some (time) discontinuity. in the transfer or transformation of thne representations. Data Logging is a more specific term implying data collection from more than one relatively low frequency source with storage of the collected data for later processingn. Hardwarne The term used for thne physical components of a computer systnem. Software This term is used to describe computer programs, whether inside or outside a computer, and whether they are machine readable or normally legible. Firmware Computer programs .stored in a semi permanent form , usually semi conductor memory, and used repeatedly without modification. Firmware can be changed only by exchanging or removing hardware.

Pre-Processor A device in a data acquisition system which performs a s _ignificant amount of data reduction , extracting specific information from_ raw signal representations ,_ in advance of the main processing operation . A preprocessor may constitute the whole of a data acquisition interface, in which case it must also perform the data acquisition task (spectrometer signal to computer representation conversion), or it may specialise solely in data treatment.

Hard Wired A preprocessor may be hard wired, that is capable of performing only certain defined tasks and no others without major physical modification. Pre-Programmed A preprocessor may be pre-programmed, that is, it can be a general purpose device incorporating specific but readily.alterable instructions to perform a particular task.

Signal Conditioning The process of altering the relationship of a transducer (spectrometer) output with respect to time or other parameters (frequency, voltage or current). Signal Processing The mechanism of. analysing, routing, sampling or changing the representation of a signal. Operational Amplifier A high gain DC voltage amplifer with high input impedance, low output impedance and the capability of producing a bipolar output.from a bipolar input. Amplifier Complex A number of operational amplifiers configured for a specific function, packaged as a single unit and used as such. Amplifier Bandwidth The range of signal frequencies over which an amplifier is capableof undistorted or unattenuated transmission. An Operational Amplifier should transmit DC voltage accurately and the upper_ (bandwidth) limit is defined as the 3 db point(factor of 2 attenuation).

  Bandwidth can vary with gain and hence Gain-Bandwidth Product can be a more useful parameter. 

Amplifier Noise This can be of two kinds, White Noise which is random signal fluctuations whose power .spectrum contains all frequencies equally over a specified bandwidth and

Pink Noise where the frequencies diminish in a specified fashion over a specified range.

Differential Amplifier An_.n(operational) amplifier which has two inputs of opposite sense gain polarity with respect to its output. Differential Ouput Amplifiers with two opposite sense outputs, also exist. Single-ended Amplifier An (operational) amplifier with a single input (or output). Analogue Signal This is a signal which can be expressed as a continuously variable math.matical function of time. Digital Signal This is a signal which represents information in a computer-compatible form as a sequence of (binary) numbers which may describe discrete samples of an analogue signal.