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Fragmentation isotope effects in the neutralization—reionization of the ethyne-d1 cation
International Journal of Mass Spectrometry and Ion Processes, 85 (1988) 91-97 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands
91
FRAGMENTATION ISOTOPE EFFECI’S IN THE NEUTRALIZATION -REIONIZATION OF THE ETHYNE d, CATION
RAYMOND E. MARCH and JOHN G. MACMILLAN Department of Chemistry, Trent University, Peterborough, Ont. K9J 7B8 (Canada) (First received 25 January 1988; in final form 14 March 1988)
ABSTRACT A pronounced isotope effect has been observed in the neutralization-reionization mass spectrum (NRMS) of CrHD? The signal intensity ratios for each of CzD+ :C2H+ and CD+ : CH+ were found to be equal to 1.91 and 2.12, respectively. It is proposed that the major isotope effects observed occur in the collision-induceddissociativeionization (CIDI) of fast neutral C,HD.
INTRODUCTION
Ethyne was selected for a recent investigation [l] of the performance of a dual-collision cell assembly with an interposed deflector electrode installed in the second field-free region of a mass spectrometer. During examination of the neutralization-reionization mass spectrometry (NRMS) [2,3] of the ethyne-d, cation, a pronounced isotope effect was observed in that the ion intensity ratios for each of CzD+ : CzH+ and CD+ : CH+ were found to be 1.91 and 2.12, respectively. An examination has been made of the variety of collisional processes which occur in NRMS using the xenon collision-induced dissociation (CID) mass spectrum of C,HD+’ and oxygen reionization maSs spectra of fast neutrals produced in metastable fragmentations. novel
EXPERIMENTAL
An upgraded mass spectrometer of reversed geometry, installed in the Ontario Regional Ion Chemistry Laboratory (ORICL) at the University of Toronto, was used for this study. This instrument has been described in detail elsewhere [4]. The second field-free region (2nd FFR) of this instrument, which is relatively long (1.025 m) has been fitted with two gas 0168-1176/88/$03.50
6 1988 Elsevier Science Publishers B.V.
92
collision cells, CC, and CC,, for the study of bimolecular processes. The collision cells are separated by a distance of 56 mm; in this region is located an ion deflector electrode similar to, though not identical with, that described elsewhere [5]. The deflector electrode may be grounded or a voltage variable to f 5 kV may be applied to it. With a voltage in excess of 3 kV applied to the deflector electrode, discrimination against charged species is total and only fast neutral species may enter CC, wherein reionization and CID1 may occur with a suitable target gas. The energy of the ionizing electron beam was held constant at 70 eV unless stated otherwise. A signal averager [6] and/or a chopper amplifier [7] were used to enhance the signal-to-noise ratio for weak signals. Ethyne-d, (82.56 at.% D), benzene1,3,5-d, (98.8 at.% D), benzene-d, (99 at.% D) and C,D, were obtained commercially [8]. The pressures of collision gases are recorded here as the gauge readings in mbar; from a previous study with this type of mass spectrometer [9], the attenuation of pressure between the collision cell and the pressure gauge was estimated to be approximately 4000 fold. RESULTS AND DISCUSSION
NRMS of the ethyne-d, cation, C, HD is A beam of mass-selected C,HD+‘ cations, m/z 27, obtained by electron impact of C,HD and accelerated through 8 kV, was directed into the first collision chamber, CC, which contained xenon as target gas at an indicated pressure of low6 mbar. The ion beam was partially neutralized in the reaction C,HD+‘+ CzHD O+ He+’
(1)
where O designates a fast neutral species. A deflector electrode located downstream of CC, and held at a potential of 5 kV created a beam of neutral molecules and radicals free of species in charged or Rydberg states [l]. The beam of neutral species then entered the second collision chamber, CC& containing oxygen at a pressure of 10m6 mbar, where a fraction of the neutral beam was reionized. As the voltage across the plates of the electrostatic analyzer was scanned, a mass-selected ion kinetic energy spectrum (MIKES) was obtained of the products of reionization C,HD” + 0, + C,HD+‘+ O2 + e-
(2)
and CIDI, to yield C*D+, C2H+, Cz , CD+, CH+, and C’; as shown in Fig. 1. The relatively large kinetic energy spread of the fragment ion peaks as compared with the reionization peak, C,HD+; is characteristic of the CID1 process. The sharp peak near E,/2 in Fig. 1 has an apparent mass-to-charge
93 C,HD”
Fig. 1. The neutralization-reionization mass spectrum of C2HD+’ derived from ethyne-d,. Ion source acceleration voltage 8 kV; Xe in collision celI 1 and 0, in collision ceII 2, each at an indicated pressure of 10e6 mbar; deflector potential 5 kV.
of 13.5 and is ascribed [lo] to the ethyne-d, dication formed from C,HD O by reactions (2) and (3)
ratio
C,HD+‘+ 0, + C2HD2+ + 0, + eAn isotope effect was observed among the fragment ions of CID1 of C2HDo in that the signal intensity ratios of C,D+ : C2H+ and CD+ : CH+ were found from peak areas to be 1.91 and 2.12, respectively. The magnitudes of these ratios indicate a marked isotope effect and were constant over a more than lO-fold variation in pressure in CC,. The miscelhtny of collisional processes in CC, and CC, must now be examined in order identify those processes contribute to overah isotope observed experimentally. Reaction in CC, accompanied by CID to form radical species, of which we need consider only those species of carbon and either hydrogen or deuterium. C,HD+‘+ Xe + C,D”‘+ Xe + H+
#a)
+ C,H”‘+ Xe + D+
(4b)
+C,D++Xe+HO
(44
+C,H++Xe+DO
W
--) CD”‘+ CH”‘+ Xe+’
(44
+ CD++ CH”‘+ Xe
@If)
+CH++CD”‘+Xe
(4g)
Reaction (4e) is described as dissociative neutralization (DN). Reaction (2)
94
in CC, is accompanied by reionization or CID1 of the fast neutral radicals, C,D”and C,HO’ C,D”‘+
0,. + C,D+ + 0, + e-
C,H”‘+ 0,
(5a)
+CD++C”+O,+e-
(5b)
+ CZH+ + 0, + e-
(6a)
+CH++C”+O,+e-
(6b)
while fast CD O* and CH O’ radicals undergo reionization CD”‘+O,+CD++O,+e-
(7a)
CH”‘+ 0, + CH+ + 0, + e-
(7b)
In addition, C,HD O may undergo CID1 to yield C,HD” + 0,
+ C,D++ Ho -t 0, + e-
(8a)
+C,H++DO+O,+e-
(8b)
+CD++CH”‘+O,+e-
(8c)
+ CH++ CD”‘+ 0, + e-
(8d)
A mass spectrum obtained by NRMS is thus derived from a number of identifiable reactions which are localized, by virtue of the deflector electrode, in either CC, or CC,. The reactions which occur in CC, and are manifested ultimately in the NR mass spectrum are neutralization [reaction (l)]; CID [reactions (4a)-(4d), (4f), (4g)]; and dissociative neutralization [reaction (4e)]. In view of the focus of this work on isotope effects, an examination was carried out only of the xenon-CID reactions. Reactions which occur in CC, are reionization [reactions (2), (Sa), (6a), (7a), (7b)] and CID1 [reactions (5b), (6b), (8a)-(Sd)]. Reionization of a species refers to a product species in an ionized state produced from a fast neutral species which existed previously either in an ionized state or as part of an ionic species. Separation of the processes which occur in CC, and CC, permits examination of the reionization process as an ionization process provided that appropriate fast neutral species may be acquired as reactant species. Pure neutral species may be acquired only as neutral fragments of the dissociation of metastable ions with lifetimes appropriate to the time window of the mass spectrometer. Thus, it is possible in this manner to acquire fast in the pure neutral species such as C,H 20 of kinetic energies of such species is limited by of the mass of masses of neutral to ionic fragment. Thus, the kinetic energy pure
95
neutral beam is precursor-dependent whereas NR product ion kinetic energy is independent of the neutral precursor. The variety of fast neutral species is also limited to isotopically pure neutral species. It is not possible to obtain a beam of pure C,HD O, a labelled or isotopically impure species, due to scrambling in the precursor metastable ion. We have not located a metastable precursor ion which contains single hydrogen and deuterium atoms and follows but a single dissociative channel to yield C, HD O. Nevertheless, it was possible to extract information on the ionization and CID1 of fast (though of lowered kinetic energy) C,HDO from examination of ionization and CID1 of pure C,H,“, pure C,D,“, and mixtures of C,Hi, C,HD”, and C,D,O obtained from metastable molecular ions of benzene, benzene-d,, and benzene-d,, respectively. Xenon-CID
of the ethyne-d,
cation, C,HD+’
From the xenon-CID mass spectrum of C,HD+; the signal intensity ratio for H+ : D+ was essentially unity (0.97); thus, reactions (4a) and (4b) do not appear to exhibit an isotope effect assuming equal collection and detection efficiencies for H+ and D+. It then follows that reactions (4a), (4b), and (4e) produce equal fluxes of C,D O* and C,H O: , Due to the lack of suitable metastable fragmentations, it has not been eossible to examine the collisional behaviour of C,DO’ and &Ho’ with oxygen [reactions (5) and (6)] but there is no evidence to suggest that the reionization or CID1 is more efficient for C,DO’ than for C,H”: On the contrary, reionization of C,H,O appears to be favoured slightly over that of C,D,O though the method of comparison as discussed below is crude. The signal intensity ratio for CzD+ to C,H+ [reactions (4c) and (4d)] was found to be 1.82 : 1.00, showing a marked propensity for the loss of Ho. The signal intensity ratio for CD+ to CH+ [reactions (4f) and (4g)] was found to be 2.66 : 1.00, showing a greater propensity for formation of the hydrogen-containing neutral. The ratio of complementary fluxes of CH O* to CD O* is also 2.66 : 1.00, which leads to the expectation that, with equal reionization efficiencies for CD O* and CH O’ in reactions (7a) and (7b), respectively, the signal intensity for CH+ will be greater than that for CD+. This expectation is contrary to the observations shown in Fig. 1. As the collection efficiency of neutral fragments formed in CC, and reionized in CC, is lower than that for fragments of species reionized in CC,, reactions (7a) and (7b) probably do not contribute significantly to the signals observed. Oxygen-reionization
of ethyne-d,,
C, HD O
An attempt to evaluate the reionization processes of C,HD O with oxygen was made as follows. It was not possible to produce a beam of fast neutral
C,HD“ either with a kinetic energy of 8 keV and free of neutral fragments, or with a lower kinetic energy of ca. 2.7 keV and free of other fast neutrals such as C,H,O and C,D,O. A compromise was arrived at wherein the reionization and CID1 contributions of the oxygen-CID energy spectrum of C,D,O were subtracted from the oxygen-CID energy spectrum of a mixture of C,HDO and C,D,“. The fast neutral alkynes were produced in the metastable decomposition of the molecular ion of benzene and deuterated benzenes [l]. For example, the metastable ( * ) molecular ion of benzene-d,, m/z 83, decomposes to produce charged and neutral fragments + C,D,H+‘* m/z 83
+ C,D,+* + C,HD” m/z 56
(9a)
+ C,D,H+’ + C,D,o m/z 55
(9b)
Charged species are removed from the beam of neutral C,HD o and C,D,O by the deflector electrode prior to CC,, so that only neutral species enter CC, where ca. 8% of the neutral species suffer single collisions with oxygen. From the reionization and CID1 behaviour of C,D,” obtained from the metastable decomposition of C,Dc* *, the intensity ratio of signals due to CZD+ and C,Dl’ was obtained as 1.000 : 0.249. The oxygen-CID1 energy spectrum of the mixture of C,HD” and C,D,” produced ion signals at each mass from m/z 24 to 28. No signals were detected from single-carbon-containing species due to the relatively low kinetic energy of the neutral species. Furthermore, as no signals were detected from the ionization of C,H; (of kinetic energy equal to 4 keV) and isotopomers, it was concluded that CID1 of C,H; did not contribute to the ion signals attributed to C,-containing ions. From the signal intensity of m/z 28, due solely to C$Dl’, the contribution of CZD+ to the signal intensity of m/z 26 was calculated and subtracted. As the signal intensity of m/z 26 is ca. one-third of that of m/z 28, stable experimental conditions were required in order to obtain reproducible results. The intensity ratio of m/z 26 : m/z 25, i.e. CZD+ and C2H+, respectively, from C,HD”, was found as 1.6 + 0.1: 1.0. As the contribution of reionized fragments to the NR mass spectrum of C,HD+’ as shown in Fig. 1 is expected to be minor, it is concluded that the observed isotope effects arise from the CID1 of C,HD O. In addition, there are similar isotope effects in the xenon-CID mass spectrum of C,HD? Complementary to the experiments described here, a brief study was made of the relationship between the signal intensity of fragment ions
t An ion kinetic energy spectrum for the corresponding loss of C,H; benzene-d, is shown in Fig. 14 of ref. 11.
and C,HD o from
97
formed in metastable decomposition, e.g. m/z 56 and m/z 55 in Eqs. (9) and the signal intensities of the oxygen-CID energy spectra of fast neutral species. &Hz, from the me&stable molecular ion of benzene, was examined together with C,D,O and C,HDO. The ratios of signal intensities of reionized species, i.e. C,Hl’, C,HD+; and C,Dc’, to those of the corresponding fragment ions were 5 X 10m5, 2.5 X 10m5, and 4 X 10m5 with an uncertainty of f0.5 x 10m5, respectively. These intensity ratios were applied to the oxygen-CID energy spectrum of a mixture of the three types of fast neutrals formed in metastable decompositions of the molecular ion of benzene-1,3,5-d, to calculate the signal intensities of the three fragment ions of m/z 53, 54, and 55. In spite of the large disparity in signal intensities of fragment ions and reionized neutrals, the calculated and observed values of fragment ion intensities agreed to within less than 20%. It is thus possible to estimate the flux of neutral species passing the deflector electrode by detecting the accompanying fragment ion formed from a metastable decomposition throughout the 2nd FFR. ACKNOWLEDGEMENTS
The financial support of the Natural Sciences and Engineering Research Council of Canada and Trent University is gratefully acknowledged. REFERENCES 1 2 3 4 5 6 7 8 9 10 11
R.E. March and A.B. Young, Int. J. Mass Spectrom. Ion Processes, 76 (1987) 11. P.O. Danis, C. Wesdemiotis and F.W. McLafferty, J. Am. Chem. Sot., 105 (1983) 454. P.O. Danis, Ph.D. Thesis, Cornell University, Ithaca, NY, 1985. A.G. Harrison, R.S. Mercer, E.J. Reiner, A.B. Young, R.K. Boyd, R.E. March and C.J. Porter, Int. J. Mass Spectrom. Ion Processes, 74 (1986) 13. J.L. Holmes and A.A. Mommers, Org. Mass Spectrom., 19 (9) (1984) 461. Tracer Northern, Middleton, WI 53562, U.S.A. V.G. Analytical Ltd., Wythenshawe, Manchester M23 9LE, Gt. Britain, Chopper Amplifier cA2. MSD Isotopes, Montreal, Quebec, Canada. T.E. Morgan, A.G. Brenton, R.E. March, F.M. Harris and J.H. Beynon, Int. J. Mass Spectrom. Ion Processes, 64 (1985) 299. RE. March, J.G. MacMillan and A.B. Young, Int. J. Mass Spectrom. Ion Processes, 82 (1988) 177. J.H. Beynon and R.G. Cooks, J. Phys. E, 7 (1974) 10.
91
FRAGMENTATION ISOTOPE EFFECI’S IN THE NEUTRALIZATION -REIONIZATION OF THE ETHYNE d, CATION
RAYMOND E. MARCH and JOHN G. MACMILLAN Department of Chemistry, Trent University, Peterborough, Ont. K9J 7B8 (Canada) (First received 25 January 1988; in final form 14 March 1988)
ABSTRACT A pronounced isotope effect has been observed in the neutralization-reionization mass spectrum (NRMS) of CrHD? The signal intensity ratios for each of CzD+ :C2H+ and CD+ : CH+ were found to be equal to 1.91 and 2.12, respectively. It is proposed that the major isotope effects observed occur in the collision-induceddissociativeionization (CIDI) of fast neutral C,HD.
INTRODUCTION
Ethyne was selected for a recent investigation [l] of the performance of a dual-collision cell assembly with an interposed deflector electrode installed in the second field-free region of a mass spectrometer. During examination of the neutralization-reionization mass spectrometry (NRMS) [2,3] of the ethyne-d, cation, a pronounced isotope effect was observed in that the ion intensity ratios for each of CzD+ : CzH+ and CD+ : CH+ were found to be 1.91 and 2.12, respectively. An examination has been made of the variety of collisional processes which occur in NRMS using the xenon collision-induced dissociation (CID) mass spectrum of C,HD+’ and oxygen reionization maSs spectra of fast neutrals produced in metastable fragmentations. novel
EXPERIMENTAL
An upgraded mass spectrometer of reversed geometry, installed in the Ontario Regional Ion Chemistry Laboratory (ORICL) at the University of Toronto, was used for this study. This instrument has been described in detail elsewhere [4]. The second field-free region (2nd FFR) of this instrument, which is relatively long (1.025 m) has been fitted with two gas 0168-1176/88/$03.50
6 1988 Elsevier Science Publishers B.V.
92
collision cells, CC, and CC,, for the study of bimolecular processes. The collision cells are separated by a distance of 56 mm; in this region is located an ion deflector electrode similar to, though not identical with, that described elsewhere [5]. The deflector electrode may be grounded or a voltage variable to f 5 kV may be applied to it. With a voltage in excess of 3 kV applied to the deflector electrode, discrimination against charged species is total and only fast neutral species may enter CC, wherein reionization and CID1 may occur with a suitable target gas. The energy of the ionizing electron beam was held constant at 70 eV unless stated otherwise. A signal averager [6] and/or a chopper amplifier [7] were used to enhance the signal-to-noise ratio for weak signals. Ethyne-d, (82.56 at.% D), benzene1,3,5-d, (98.8 at.% D), benzene-d, (99 at.% D) and C,D, were obtained commercially [8]. The pressures of collision gases are recorded here as the gauge readings in mbar; from a previous study with this type of mass spectrometer [9], the attenuation of pressure between the collision cell and the pressure gauge was estimated to be approximately 4000 fold. RESULTS AND DISCUSSION
NRMS of the ethyne-d, cation, C, HD is A beam of mass-selected C,HD+‘ cations, m/z 27, obtained by electron impact of C,HD and accelerated through 8 kV, was directed into the first collision chamber, CC, which contained xenon as target gas at an indicated pressure of low6 mbar. The ion beam was partially neutralized in the reaction C,HD+‘+ CzHD O+ He+’
(1)
where O designates a fast neutral species. A deflector electrode located downstream of CC, and held at a potential of 5 kV created a beam of neutral molecules and radicals free of species in charged or Rydberg states [l]. The beam of neutral species then entered the second collision chamber, CC& containing oxygen at a pressure of 10m6 mbar, where a fraction of the neutral beam was reionized. As the voltage across the plates of the electrostatic analyzer was scanned, a mass-selected ion kinetic energy spectrum (MIKES) was obtained of the products of reionization C,HD” + 0, + C,HD+‘+ O2 + e-
(2)
and CIDI, to yield C*D+, C2H+, Cz , CD+, CH+, and C’; as shown in Fig. 1. The relatively large kinetic energy spread of the fragment ion peaks as compared with the reionization peak, C,HD+; is characteristic of the CID1 process. The sharp peak near E,/2 in Fig. 1 has an apparent mass-to-charge
93 C,HD”
Fig. 1. The neutralization-reionization mass spectrum of C2HD+’ derived from ethyne-d,. Ion source acceleration voltage 8 kV; Xe in collision celI 1 and 0, in collision ceII 2, each at an indicated pressure of 10e6 mbar; deflector potential 5 kV.
of 13.5 and is ascribed [lo] to the ethyne-d, dication formed from C,HD O by reactions (2) and (3)
ratio
C,HD+‘+ 0, + C2HD2+ + 0, + eAn isotope effect was observed among the fragment ions of CID1 of C2HDo in that the signal intensity ratios of C,D+ : C2H+ and CD+ : CH+ were found from peak areas to be 1.91 and 2.12, respectively. The magnitudes of these ratios indicate a marked isotope effect and were constant over a more than lO-fold variation in pressure in CC,. The miscelhtny of collisional processes in CC, and CC, must now be examined in order identify those processes contribute to overah isotope observed experimentally. Reaction in CC, accompanied by CID to form radical species, of which we need consider only those species of carbon and either hydrogen or deuterium. C,HD+‘+ Xe + C,D”‘+ Xe + H+
#a)
+ C,H”‘+ Xe + D+
(4b)
+C,D++Xe+HO
(44
+C,H++Xe+DO
W
--) CD”‘+ CH”‘+ Xe+’
(44
+ CD++ CH”‘+ Xe
@If)
+CH++CD”‘+Xe
(4g)
Reaction (4e) is described as dissociative neutralization (DN). Reaction (2)
94
in CC, is accompanied by reionization or CID1 of the fast neutral radicals, C,D”and C,HO’ C,D”‘+
0,. + C,D+ + 0, + e-
C,H”‘+ 0,
(5a)
+CD++C”+O,+e-
(5b)
+ CZH+ + 0, + e-
(6a)
+CH++C”+O,+e-
(6b)
while fast CD O* and CH O’ radicals undergo reionization CD”‘+O,+CD++O,+e-
(7a)
CH”‘+ 0, + CH+ + 0, + e-
(7b)
In addition, C,HD O may undergo CID1 to yield C,HD” + 0,
+ C,D++ Ho -t 0, + e-
(8a)
+C,H++DO+O,+e-
(8b)
+CD++CH”‘+O,+e-
(8c)
+ CH++ CD”‘+ 0, + e-
(8d)
A mass spectrum obtained by NRMS is thus derived from a number of identifiable reactions which are localized, by virtue of the deflector electrode, in either CC, or CC,. The reactions which occur in CC, and are manifested ultimately in the NR mass spectrum are neutralization [reaction (l)]; CID [reactions (4a)-(4d), (4f), (4g)]; and dissociative neutralization [reaction (4e)]. In view of the focus of this work on isotope effects, an examination was carried out only of the xenon-CID reactions. Reactions which occur in CC, are reionization [reactions (2), (Sa), (6a), (7a), (7b)] and CID1 [reactions (5b), (6b), (8a)-(Sd)]. Reionization of a species refers to a product species in an ionized state produced from a fast neutral species which existed previously either in an ionized state or as part of an ionic species. Separation of the processes which occur in CC, and CC, permits examination of the reionization process as an ionization process provided that appropriate fast neutral species may be acquired as reactant species. Pure neutral species may be acquired only as neutral fragments of the dissociation of metastable ions with lifetimes appropriate to the time window of the mass spectrometer. Thus, it is possible in this manner to acquire fast in the pure neutral species such as C,H 20 of kinetic energies of such species is limited by of the mass of masses of neutral to ionic fragment. Thus, the kinetic energy pure
95
neutral beam is precursor-dependent whereas NR product ion kinetic energy is independent of the neutral precursor. The variety of fast neutral species is also limited to isotopically pure neutral species. It is not possible to obtain a beam of pure C,HD O, a labelled or isotopically impure species, due to scrambling in the precursor metastable ion. We have not located a metastable precursor ion which contains single hydrogen and deuterium atoms and follows but a single dissociative channel to yield C, HD O. Nevertheless, it was possible to extract information on the ionization and CID1 of fast (though of lowered kinetic energy) C,HDO from examination of ionization and CID1 of pure C,H,“, pure C,D,“, and mixtures of C,Hi, C,HD”, and C,D,O obtained from metastable molecular ions of benzene, benzene-d,, and benzene-d,, respectively. Xenon-CID
of the ethyne-d,
cation, C,HD+’
From the xenon-CID mass spectrum of C,HD+; the signal intensity ratio for H+ : D+ was essentially unity (0.97); thus, reactions (4a) and (4b) do not appear to exhibit an isotope effect assuming equal collection and detection efficiencies for H+ and D+. It then follows that reactions (4a), (4b), and (4e) produce equal fluxes of C,D O* and C,H O: , Due to the lack of suitable metastable fragmentations, it has not been eossible to examine the collisional behaviour of C,DO’ and &Ho’ with oxygen [reactions (5) and (6)] but there is no evidence to suggest that the reionization or CID1 is more efficient for C,DO’ than for C,H”: On the contrary, reionization of C,H,O appears to be favoured slightly over that of C,D,O though the method of comparison as discussed below is crude. The signal intensity ratio for CzD+ to C,H+ [reactions (4c) and (4d)] was found to be 1.82 : 1.00, showing a marked propensity for the loss of Ho. The signal intensity ratio for CD+ to CH+ [reactions (4f) and (4g)] was found to be 2.66 : 1.00, showing a greater propensity for formation of the hydrogen-containing neutral. The ratio of complementary fluxes of CH O* to CD O* is also 2.66 : 1.00, which leads to the expectation that, with equal reionization efficiencies for CD O* and CH O’ in reactions (7a) and (7b), respectively, the signal intensity for CH+ will be greater than that for CD+. This expectation is contrary to the observations shown in Fig. 1. As the collection efficiency of neutral fragments formed in CC, and reionized in CC, is lower than that for fragments of species reionized in CC,, reactions (7a) and (7b) probably do not contribute significantly to the signals observed. Oxygen-reionization
of ethyne-d,,
C, HD O
An attempt to evaluate the reionization processes of C,HD O with oxygen was made as follows. It was not possible to produce a beam of fast neutral
C,HD“ either with a kinetic energy of 8 keV and free of neutral fragments, or with a lower kinetic energy of ca. 2.7 keV and free of other fast neutrals such as C,H,O and C,D,O. A compromise was arrived at wherein the reionization and CID1 contributions of the oxygen-CID energy spectrum of C,D,O were subtracted from the oxygen-CID energy spectrum of a mixture of C,HDO and C,D,“. The fast neutral alkynes were produced in the metastable decomposition of the molecular ion of benzene and deuterated benzenes [l]. For example, the metastable ( * ) molecular ion of benzene-d,, m/z 83, decomposes to produce charged and neutral fragments + C,D,H+‘* m/z 83
+ C,D,+* + C,HD” m/z 56
(9a)
+ C,D,H+’ + C,D,o m/z 55
(9b)
Charged species are removed from the beam of neutral C,HD o and C,D,O by the deflector electrode prior to CC,, so that only neutral species enter CC, where ca. 8% of the neutral species suffer single collisions with oxygen. From the reionization and CID1 behaviour of C,D,” obtained from the metastable decomposition of C,Dc* *, the intensity ratio of signals due to CZD+ and C,Dl’ was obtained as 1.000 : 0.249. The oxygen-CID1 energy spectrum of the mixture of C,HD” and C,D,” produced ion signals at each mass from m/z 24 to 28. No signals were detected from single-carbon-containing species due to the relatively low kinetic energy of the neutral species. Furthermore, as no signals were detected from the ionization of C,H; (of kinetic energy equal to 4 keV) and isotopomers, it was concluded that CID1 of C,H; did not contribute to the ion signals attributed to C,-containing ions. From the signal intensity of m/z 28, due solely to C$Dl’, the contribution of CZD+ to the signal intensity of m/z 26 was calculated and subtracted. As the signal intensity of m/z 26 is ca. one-third of that of m/z 28, stable experimental conditions were required in order to obtain reproducible results. The intensity ratio of m/z 26 : m/z 25, i.e. CZD+ and C2H+, respectively, from C,HD”, was found as 1.6 + 0.1: 1.0. As the contribution of reionized fragments to the NR mass spectrum of C,HD+’ as shown in Fig. 1 is expected to be minor, it is concluded that the observed isotope effects arise from the CID1 of C,HD O. In addition, there are similar isotope effects in the xenon-CID mass spectrum of C,HD? Complementary to the experiments described here, a brief study was made of the relationship between the signal intensity of fragment ions
t An ion kinetic energy spectrum for the corresponding loss of C,H; benzene-d, is shown in Fig. 14 of ref. 11.
and C,HD o from
97
formed in metastable decomposition, e.g. m/z 56 and m/z 55 in Eqs. (9) and the signal intensities of the oxygen-CID energy spectra of fast neutral species. &Hz, from the me&stable molecular ion of benzene, was examined together with C,D,O and C,HDO. The ratios of signal intensities of reionized species, i.e. C,Hl’, C,HD+; and C,Dc’, to those of the corresponding fragment ions were 5 X 10m5, 2.5 X 10m5, and 4 X 10m5 with an uncertainty of f0.5 x 10m5, respectively. These intensity ratios were applied to the oxygen-CID energy spectrum of a mixture of the three types of fast neutrals formed in metastable decompositions of the molecular ion of benzene-1,3,5-d, to calculate the signal intensities of the three fragment ions of m/z 53, 54, and 55. In spite of the large disparity in signal intensities of fragment ions and reionized neutrals, the calculated and observed values of fragment ion intensities agreed to within less than 20%. It is thus possible to estimate the flux of neutral species passing the deflector electrode by detecting the accompanying fragment ion formed from a metastable decomposition throughout the 2nd FFR. ACKNOWLEDGEMENTS
The financial support of the Natural Sciences and Engineering Research Council of Canada and Trent University is gratefully acknowledged. REFERENCES 1 2 3 4 5 6 7 8 9 10 11
R.E. March and A.B. Young, Int. J. Mass Spectrom. Ion Processes, 76 (1987) 11. P.O. Danis, C. Wesdemiotis and F.W. McLafferty, J. Am. Chem. Sot., 105 (1983) 454. P.O. Danis, Ph.D. Thesis, Cornell University, Ithaca, NY, 1985. A.G. Harrison, R.S. Mercer, E.J. Reiner, A.B. Young, R.K. Boyd, R.E. March and C.J. Porter, Int. J. Mass Spectrom. Ion Processes, 74 (1986) 13. J.L. Holmes and A.A. Mommers, Org. Mass Spectrom., 19 (9) (1984) 461. Tracer Northern, Middleton, WI 53562, U.S.A. V.G. Analytical Ltd., Wythenshawe, Manchester M23 9LE, Gt. Britain, Chopper Amplifier cA2. MSD Isotopes, Montreal, Quebec, Canada. T.E. Morgan, A.G. Brenton, R.E. March, F.M. Harris and J.H. Beynon, Int. J. Mass Spectrom. Ion Processes, 64 (1985) 299. RE. March, J.G. MacMillan and A.B. Young, Int. J. Mass Spectrom. Ion Processes, 82 (1988) 177. J.H. Beynon and R.G. Cooks, J. Phys. E, 7 (1974) 10.