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Measurements of thermal energy neon ion—neutral reaction rate coefficients and product ion distributions
CHEMICAL PHYSICS LETTERS
Volume 60, number 3
MEASUREMENTS COEFFICIENTS A.B. RAKSHIT
OF TFIERMAL ENERGY
NEON ION-NEUTRAL
IS January1979
REACI’IONRATE
AND PRODUCT ION DISTRIBUTIONS and N.D. TWIDDY
Depsrtmentof Physics, lkiversi@ GSege of WaZes, P~gia&ARberyztwyrh.DyfedSYZ33B2,EJK Received25 August 1978 Revisedmanuscriptrcccivcd27 November 1978 Reactionrate coefficientsand production distributionshave been meazued for the reactionof Ne+ with Hz, N+, CO, C02, NzO , CH4,02, NO, NHa, Sot, CHJCI, COS, Hz0 and CzH4 at 300 K usinga selectedion fiow tube (SIFT) apparatus_In most casesthe major reactionchannelinvolvesdissociativeionizationwhilefor N2. CO+, H20, CH+ =nd CH3Q thesereactionsproceedmainIyor exdusively by simplechargetransfer_For H2 the processis exch&veIy hydrogenatom abstractiorzThe measuredrate coefficientsare comparedwith the vaIuesgivenby the Langevinand average-dipoleorientation theorks of ion-molecrle collisions.In gcneratthe reactionprobability(ratio of measuredrate to the Langevinor ADO rate) is greaterfor the dissociativeionizationreactions,althoughHz0 is an exception with quite fast simplechargetransfer.
1_ Introduction Earlier measurements of thermal enera/ neon ionmolecule reaction rates obtained in this laboratory in a flowing afterglow ?ppamtus [I ] did not in general provide product ion distributions. However the se&ted ion flow tube (SIFT) [Z] makes the measurement of product distributions relatively straightforward and the earlier work with neon ions has been extended on the Aberystwyth SIFT apparatus to obtain product ion distriiutions_
2Expeliinent This apparatus has already been described in Glosik et al- [3] and R&shit et aI_ [4] _ In the present work the neon ions were generated from neon gas (BOC special grade) in an EB$ Iow pressure electron impact source using an eIectron energy = 24 eV_ The mass selected Ne ions (20 amu isotope) were injected into the helitui carrier gas flow and thermal&d in co&ion with the helium carrier gas_ The neutral reactant gas was introduced in measured rate downstream some 722 cm f%om the ENL mass spectrometer sampliug orifice. The ion signal3 were measured with a conven-
tional channeltron/pulse counting system. Reaction rate coefficients were determined from the exponential decay of the primary ion count with neutral reactant ffow rate.
3. AnaIysis
The product ion distriiutions were obtained using the procedure adopted by Adams and Smith [S] _ This involves plotting rhe percentage of the various product ions as a fiinction of reactant gas Llow rate and extrapolating the resulting curves to zero flow rate to determine the products of the initial reaction, since the curves of ions produced in subsequent reactions with the neutral reactant will extrapolate to zero at zero neutral reactant fIow rate. However in a few cases, namely. CO,, NH, and C!I+Cl, where fast secondary reactionsoccur, thisprocedure gave some ambiguity because of the large curvature of the product ion extrapolation near to zero reactant flow rate- This ambiguity was overcome by applying a curve fitting procedure to the secondary ion intensity curves using measured reaction rates for the primary and secondary reactions. Thisisillustmtedinfigs. laand lbforNe++C02. Fig. la shows the exponential decay of the Ne+ ion
Volume 60, numbs
CHEMKAL
3
PHYSICS LETTERS
IS January 1979
the neutral reactant CO,, together with ion production curves for CO; and CO*, the latter having a very pronounced negative slope indicating that the CO+ is undergoing a fast secondary reaction with ‘&e neutral reactant CO,. Furthermore the absence of any additional product ion indicates that the CO+ must be being converted to CO;The plot of the percentage product-ion versus reactant flow rate is shown in fig_ lb and this ilhrstrates clearly the difficulty in extrapolating the two curves to zero CO2 flow rate. Allowing for the experimental scatter, the initial product ion distribution could be inferred to be anywhere between 100% and 50% for CO+ with corresponding values of 0% and 5% for CO;. This uncertainty arises because of the large curvature near the origin. This can be largely resolved by using the chemical kinetic equations for the formation and loss of the product ions CO* and CO;, together with the known or measured reaction rates for the primary and secondary reactions, to apply a curve fitting procedure to determine the initial product ion distribution_ This process is illustrated in fig_ I.a which shows calculated CO+ growth curves for different selected percentages of initial CO+ production (50% to 100% in steps of 10%). The conclusion can then be drawn that CO* is the major initial product ion of the reaction (- _ 90%). In this particular case the scatter on the experimental points prevents a decision on whether CO+ is the only initial product ion. with
FEKmRs-*a#
I
-I
at3
I
as
b
4. Results and discussion a0 1. (a) Ne+ + CO, -+ CO+ + 0 f Ne, Ne* f CO2 -+ CO; + Ne. Ion signah versus CO2 flow rate (experimental points)_ The rate coefficient is obtained from the slope of the Nef dccay. The pronouncednegativestope of the Co+ data indicates that the CO+ formed is reacting rapid& with Co2 to form CO:_ The fuIl curves are computed product ion growth curves. The CO+ CUIV~S are for cases in which the CO+ production is 50100% (in stepsof 10%) of the total secondary ion production. Comparison with the experimental data shows that CO” is the major secondaryion (> 90%).@) mot of the product IOILS (secondary and tertizw), expressed as a pcccmtage of the total ion production versus CO2 flow rate. The large. curvature at low CO2 ff0w rates prevents satisfactory extrapolation to zero CO2 flow rate in order to distinguish between secondary and tertiary ions. This is resohed by using l Ae curve fitting procedure illustrated in fig. la. Fig
In general there is good agreement with the earlier rate coefficients from this laboratory cl] and also with the recent product distribution obtained by Anicich et al. [6] who studied Ne+ reactions with N2, Oz. CO, NO, CO, and N,O using a tandem ion cyclotron resonance method (TICR), see table 1. For the diatomics, N2, CO, Hz, 0, and NO, the reaction rates for the first three are very slow * lo-l3 cm3 s-r, due to the very small Franck-Condon factors for resonant charge exchange [I]. The reactions proceed by sirnpIe charge transfer for N2 and CO and by hydrogen atom abstraction for HZ. For 0, and NO the reaction rates are some two orders of magnitude fster, the reaction proceeding by dissociative ionization. 401
8(-11)
Nc++CO~~CO++O+Nc+2,08cV
NB++ NH34 NH; + M+ No + 5,6CV -tNH$“Ne+l1,37uV + NII++ f12+ NC+ 4.52cV
12 w2
86
100’
8,8(-10)
NC++ Hl 0 -I U20’ + No4 8,98oV (-10)
47 47 I
1,4(-9)
ND~~CCOS~CO~+S~NO~~,~~OV 4s” cCO+Nc+8,04V 4CS++O’tNe+3,31 oV -1COS*4 No+ lo,39aV
-+ N1O+ + NC+ 8.66 CV
55 22 18 -3 m2
100
91 9
Ne++NN1O-tNO++NtNu+7.32oV 4(-10) -,N++NO+No+2,0SoV -tN++O+No+4,24eV %+N2+Ne+6,19CV -+O
-rOf+CO+No+2,49cV -(CO;+Nc+7.89cV
lS(-10)
Nu++NO+N’+O+Ne+4.7cV -,O+tNtNNct 1.38cV ~NO”+Nct12,3lcV
100
171
111
2(-W (11
8,2(-10) [ 131 7,4(-10) [ 141
3.4(-10) [7]
5(-11) 5(-11)
l.S(-10) [ 71 1,2(-10) [l] 9,2(-11) (121
5,8(-11) \7] W-11) [l] G,S(-11)[lo] S,O(-11)[ll]
-
15
48i61
100 [6] <3 c3
100[6] <3 c3
c3
100 [6]
2,16
1.47
(continued on next pngC)
2J(-9)
1.13(-9)
5.6
3.0
1.70
0,81
194
(u(n3)
1,45
0.718
0,17
0.16
0.11
PD Mw)
L84
1,6(-9)
1J (-9)
-
8,9(-10)
-
-
-
9,6(-10)
w*-
kADd
9.16(-10) 2,31(-g)
1.43(-9)
1.09(-9)
1,02(-9)
8,7(-IO)
8,4(-10)
9,1(-10)
c I(-14) [9] c l(-12) [7] c l(-12) [I]
100
< 3(-13)
6,2(-11)
1,8(-g)
C3(-13)[1] < 8(-12) [8]
9,5(-10)
100
100 (6)
G I(-12) (71 < I(-13) [l]
< 3,2(-13)
product Ion distlibrltion (%) --
rat0 cocfficicnt C)
AL
NC++ Ha + Nell++ II + 6.12 oV
100
product ion di8tribUtiOn(%I
OthCrIcHl1t8
< 3,2(-13)
rat0 cocflicicnt C) -_II-
Prcscnt result
NC’* CO 3 CO’ + NC+ 7,59 CV
Rcoctlon
Mcnsuromontsof rntc cocfficicntfiand product ion distributions of the ruactlon of NC’ ions at 300 K
Tablo 1
VorUme60, number3
CHEMICAL
I
I
G: A
T x d
I
I
PHYSICS L.ExTERs
15 January 1979
For the hnear triatomics N20, CO, and COS the reactions again a!l involve dissociativeYionization, for N20 the favoured channel invofvesthe breaking of the N-N bond giving 55% NO+; for CO, the exclusive reaction channel involves the breaking of the C-O bond (100% CO+) while for OCS the C-S bond is broken with an equal probability of ionization of the CO or S frapents (47% CO+, 47% S). The reaction probability, i.e. the ratio of measured raction rate to the Langevin rate (or the ADO rate if the molecule has a permanent magnetic dipole moment) has a value of 0.86 for COS. For Hz0 only simple chrargetransfer occurs, the reaction rate is in good agreement with that of Bolden and Twiddy [ 131 and yields a reaction probability of 0.38. For NH, the reaction is mainly dissociativeionization giving 86% e and the reaction probability is 0.12.
For CH$I the reaction involvesboth simple charge transfer and dissociativeionization in approximately equal measure (42~56%) and has a reaction probability of unity- However for CH4, although the reaction is similarly divided between simple charge transfer and dissociativeionization the reaction probability is only 0.013. For SO, the reaction is exclusively dissociativeionization giving SO+ with a reaction probability of 1-l 5. For C2Hq the reaction is largely by dissociativeion$ation to C& with 18% simple charge transfer and has a reaction probability of O-86_
Acknowledgement The authors wish to thank Drs. K. Birkinshaw and D_ Lister for valuable discussions.ML D. Wareing for his assistancewith ‘rheexperiments and Dr. M. Tichy for programming the curve fitting process. Ackn~wledgements are also due to the Science Research Council for a post-doctoral researchassociateshipfor one of us (A.B.R.). References R.S. Hemsworth, RX. Bolden,MJ. shaw ami N.D. Twiddy, Ckem. Pkys. Letters 5 (1970) 237. [ 21 N-G. Adams and D. Smith, htem. J. Mass Spe&Om. Ion Pkys. 21<1976) 349. [l]
403
Vo!ume 60, number 3
CHEMICAL
PHYSICS LETl-ERS
[ 3 ] J. GIosik, A-B. Raksfri; W.D. Twiddy, N-G. Adams and
[4] I51 [6] [ 71 [8] [9] [ 1Oi
D. Smith, J. Phys. B (1978). to be published. A-B. Rakshit. H.M.P. Stock, D.P. Wareing and N.D. Twiddy, J. Phys. B (1978), to he published. N-G- Adams and D. Smith, J. Phys. B 9 (1976) 1439. V.G. Anicich, J.B. Laudenslager znd W.T. Hunfress Jr., J. Chem. Phys. 67 (1977) 4340. J-B. JI.audens!dager, M-T. Boaiea and W-T. Huntress Jr., J. Chem. Phys 61(1974) 4600. V. Aquilanti, A- Galli, k GriordiniGuidoni and G.G. Volpi, J. Chem. Phys. 43 (1965) 1969. D-L Albritton, M. McFarland and A.J-..Schmeltekopf, J. Chem. Phys. 58 (1973) 4036. RC Bolden, RS. Hemsworth, M.J. Shaw and N.D. Twiddy, 3. Phys. B 3 (1970) 45.
[ll
15 January 1979
] N-G. Adams,A.G. Dean and D. Smith, Intern- J. Mass
Spectrom. Ion Phys. 10 (1972) 63. T.F. Moran and L Friedrn~, J. Chem. Phys 45 (1966) 3837. [I31 R.C Bolden and N.D. Twiddy, Faraday Discussions them. Sot. 53 (1972) 192. (141 C-J. Howard, H.W. R-undeB and F. Kaufman. J. Chem. Phys. 53 (1970) 3745. [IS] UT. Bower and D.D. EIIeman, Chem. Phys Letters 16 (1972) 482. [ 161 E.G. Jones and A.G. Harrison, Intern. J. Mass Speceom. Ion Phys. 6 (1971) 77. j12]
Volume 60, number 3
MEASUREMENTS COEFFICIENTS A.B. RAKSHIT
OF TFIERMAL ENERGY
NEON ION-NEUTRAL
IS January1979
REACI’IONRATE
AND PRODUCT ION DISTRIBUTIONS and N.D. TWIDDY
Depsrtmentof Physics, lkiversi@ GSege of WaZes, P~gia&ARberyztwyrh.DyfedSYZ33B2,EJK Received25 August 1978 Revisedmanuscriptrcccivcd27 November 1978 Reactionrate coefficientsand production distributionshave been meazued for the reactionof Ne+ with Hz, N+, CO, C02, NzO , CH4,02, NO, NHa, Sot, CHJCI, COS, Hz0 and CzH4 at 300 K usinga selectedion fiow tube (SIFT) apparatus_In most casesthe major reactionchannelinvolvesdissociativeionizationwhilefor N2. CO+, H20, CH+ =nd CH3Q thesereactionsproceedmainIyor exdusively by simplechargetransfer_For H2 the processis exch&veIy hydrogenatom abstractiorzThe measuredrate coefficientsare comparedwith the vaIuesgivenby the Langevinand average-dipoleorientation theorks of ion-molecrle collisions.In gcneratthe reactionprobability(ratio of measuredrate to the Langevinor ADO rate) is greaterfor the dissociativeionizationreactions,althoughHz0 is an exception with quite fast simplechargetransfer.
1_ Introduction Earlier measurements of thermal enera/ neon ionmolecule reaction rates obtained in this laboratory in a flowing afterglow ?ppamtus [I ] did not in general provide product ion distributions. However the se&ted ion flow tube (SIFT) [Z] makes the measurement of product distributions relatively straightforward and the earlier work with neon ions has been extended on the Aberystwyth SIFT apparatus to obtain product ion distriiutions_
2Expeliinent This apparatus has already been described in Glosik et al- [3] and R&shit et aI_ [4] _ In the present work the neon ions were generated from neon gas (BOC special grade) in an EB$ Iow pressure electron impact source using an eIectron energy = 24 eV_ The mass selected Ne ions (20 amu isotope) were injected into the helitui carrier gas flow and thermal&d in co&ion with the helium carrier gas_ The neutral reactant gas was introduced in measured rate downstream some 722 cm f%om the ENL mass spectrometer sampliug orifice. The ion signal3 were measured with a conven-
tional channeltron/pulse counting system. Reaction rate coefficients were determined from the exponential decay of the primary ion count with neutral reactant ffow rate.
3. AnaIysis
The product ion distriiutions were obtained using the procedure adopted by Adams and Smith [S] _ This involves plotting rhe percentage of the various product ions as a fiinction of reactant gas Llow rate and extrapolating the resulting curves to zero flow rate to determine the products of the initial reaction, since the curves of ions produced in subsequent reactions with the neutral reactant will extrapolate to zero at zero neutral reactant fIow rate. However in a few cases, namely. CO,, NH, and C!I+Cl, where fast secondary reactionsoccur, thisprocedure gave some ambiguity because of the large curvature of the product ion extrapolation near to zero reactant flow rate- This ambiguity was overcome by applying a curve fitting procedure to the secondary ion intensity curves using measured reaction rates for the primary and secondary reactions. Thisisillustmtedinfigs. laand lbforNe++C02. Fig. la shows the exponential decay of the Ne+ ion
Volume 60, numbs
CHEMKAL
3
PHYSICS LETTERS
IS January 1979
the neutral reactant CO,, together with ion production curves for CO; and CO*, the latter having a very pronounced negative slope indicating that the CO+ is undergoing a fast secondary reaction with ‘&e neutral reactant CO,. Furthermore the absence of any additional product ion indicates that the CO+ must be being converted to CO;The plot of the percentage product-ion versus reactant flow rate is shown in fig_ lb and this ilhrstrates clearly the difficulty in extrapolating the two curves to zero CO2 flow rate. Allowing for the experimental scatter, the initial product ion distribution could be inferred to be anywhere between 100% and 50% for CO+ with corresponding values of 0% and 5% for CO;. This uncertainty arises because of the large curvature near the origin. This can be largely resolved by using the chemical kinetic equations for the formation and loss of the product ions CO* and CO;, together with the known or measured reaction rates for the primary and secondary reactions, to apply a curve fitting procedure to determine the initial product ion distribution_ This process is illustrated in fig_ I.a which shows calculated CO+ growth curves for different selected percentages of initial CO+ production (50% to 100% in steps of 10%). The conclusion can then be drawn that CO* is the major initial product ion of the reaction (- _ 90%). In this particular case the scatter on the experimental points prevents a decision on whether CO+ is the only initial product ion. with
FEKmRs-*a#
I
-I
at3
I
as
b
4. Results and discussion a0 1. (a) Ne+ + CO, -+ CO+ + 0 f Ne, Ne* f CO2 -+ CO; + Ne. Ion signah versus CO2 flow rate (experimental points)_ The rate coefficient is obtained from the slope of the Nef dccay. The pronouncednegativestope of the Co+ data indicates that the CO+ formed is reacting rapid& with Co2 to form CO:_ The fuIl curves are computed product ion growth curves. The CO+ CUIV~S are for cases in which the CO+ production is 50100% (in stepsof 10%) of the total secondary ion production. Comparison with the experimental data shows that CO” is the major secondaryion (> 90%).@) mot of the product IOILS (secondary and tertizw), expressed as a pcccmtage of the total ion production versus CO2 flow rate. The large. curvature at low CO2 ff0w rates prevents satisfactory extrapolation to zero CO2 flow rate in order to distinguish between secondary and tertiary ions. This is resohed by using l Ae curve fitting procedure illustrated in fig. la. Fig
In general there is good agreement with the earlier rate coefficients from this laboratory cl] and also with the recent product distribution obtained by Anicich et al. [6] who studied Ne+ reactions with N2, Oz. CO, NO, CO, and N,O using a tandem ion cyclotron resonance method (TICR), see table 1. For the diatomics, N2, CO, Hz, 0, and NO, the reaction rates for the first three are very slow * lo-l3 cm3 s-r, due to the very small Franck-Condon factors for resonant charge exchange [I]. The reactions proceed by sirnpIe charge transfer for N2 and CO and by hydrogen atom abstraction for HZ. For 0, and NO the reaction rates are some two orders of magnitude fster, the reaction proceeding by dissociative ionization. 401
8(-11)
Nc++CO~~CO++O+Nc+2,08cV
NB++ NH34 NH; + M+ No + 5,6CV -tNH$“Ne+l1,37uV + NII++ f12+ NC+ 4.52cV
12 w2
86
100’
8,8(-10)
NC++ Hl 0 -I U20’ + No4 8,98oV (-10)
47 47 I
1,4(-9)
ND~~CCOS~CO~+S~NO~~,~~OV 4s” cCO+Nc+8,04V 4CS++O’tNe+3,31 oV -1COS*4 No+ lo,39aV
-+ N1O+ + NC+ 8.66 CV
55 22 18 -3 m2
100
91 9
Ne++NN1O-tNO++NtNu+7.32oV 4(-10) -,N++NO+No+2,0SoV -tN++O+No+4,24eV %+N2+Ne+6,19CV -+O
-rOf+CO+No+2,49cV -(CO;+Nc+7.89cV
lS(-10)
Nu++NO+N’+O+Ne+4.7cV -,O+tNtNNct 1.38cV ~NO”+Nct12,3lcV
100
171
111
2(-W (11
8,2(-10) [ 131 7,4(-10) [ 141
3.4(-10) [7]
5(-11) 5(-11)
l.S(-10) [ 71 1,2(-10) [l] 9,2(-11) (121
5,8(-11) \7] W-11) [l] G,S(-11)[lo] S,O(-11)[ll]
-
15
48i61
100 [6] <3 c3
100[6] <3 c3
c3
100 [6]
2,16
1.47
(continued on next pngC)
2J(-9)
1.13(-9)
5.6
3.0
1.70
0,81
194
(u(n3)
1,45
0.718
0,17
0.16
0.11
PD Mw)
L84
1,6(-9)
1J (-9)
-
8,9(-10)
-
-
-
9,6(-10)
w*-
kADd
9.16(-10) 2,31(-g)
1.43(-9)
1.09(-9)
1,02(-9)
8,7(-IO)
8,4(-10)
9,1(-10)
c I(-14) [9] c l(-12) [7] c l(-12) [I]
100
< 3(-13)
6,2(-11)
1,8(-g)
C3(-13)[1] < 8(-12) [8]
9,5(-10)
100
100 (6)
G I(-12) (71 < I(-13) [l]
< 3,2(-13)
product Ion distlibrltion (%) --
rat0 cocfficicnt C)
AL
NC++ Ha + Nell++ II + 6.12 oV
100
product ion di8tribUtiOn(%I
OthCrIcHl1t8
< 3,2(-13)
rat0 cocflicicnt C) -_II-
Prcscnt result
NC’* CO 3 CO’ + NC+ 7,59 CV
Rcoctlon
Mcnsuromontsof rntc cocfficicntfiand product ion distributions of the ruactlon of NC’ ions at 300 K
Tablo 1
VorUme60, number3
CHEMICAL
I
I
G: A
T x d
I
I
PHYSICS L.ExTERs
15 January 1979
For the hnear triatomics N20, CO, and COS the reactions again a!l involve dissociativeYionization, for N20 the favoured channel invofvesthe breaking of the N-N bond giving 55% NO+; for CO, the exclusive reaction channel involves the breaking of the C-O bond (100% CO+) while for OCS the C-S bond is broken with an equal probability of ionization of the CO or S frapents (47% CO+, 47% S). The reaction probability, i.e. the ratio of measured raction rate to the Langevin rate (or the ADO rate if the molecule has a permanent magnetic dipole moment) has a value of 0.86 for COS. For Hz0 only simple chrargetransfer occurs, the reaction rate is in good agreement with that of Bolden and Twiddy [ 131 and yields a reaction probability of 0.38. For NH, the reaction is mainly dissociativeionization giving 86% e and the reaction probability is 0.12.
For CH$I the reaction involvesboth simple charge transfer and dissociativeionization in approximately equal measure (42~56%) and has a reaction probability of unity- However for CH4, although the reaction is similarly divided between simple charge transfer and dissociativeionization the reaction probability is only 0.013. For SO, the reaction is exclusively dissociativeionization giving SO+ with a reaction probability of 1-l 5. For C2Hq the reaction is largely by dissociativeion$ation to C& with 18% simple charge transfer and has a reaction probability of O-86_
Acknowledgement The authors wish to thank Drs. K. Birkinshaw and D_ Lister for valuable discussions.ML D. Wareing for his assistancewith ‘rheexperiments and Dr. M. Tichy for programming the curve fitting process. Ackn~wledgements are also due to the Science Research Council for a post-doctoral researchassociateshipfor one of us (A.B.R.). References R.S. Hemsworth, RX. Bolden,MJ. shaw ami N.D. Twiddy, Ckem. Pkys. Letters 5 (1970) 237. [ 21 N-G. Adams and D. Smith, htem. J. Mass Spe&Om. Ion Pkys. 21<1976) 349. [l]
403
Vo!ume 60, number 3
CHEMICAL
PHYSICS LETl-ERS
[ 3 ] J. GIosik, A-B. Raksfri; W.D. Twiddy, N-G. Adams and
[4] I51 [6] [ 71 [8] [9] [ 1Oi
D. Smith, J. Phys. B (1978). to be published. A-B. Rakshit. H.M.P. Stock, D.P. Wareing and N.D. Twiddy, J. Phys. B (1978), to he published. N-G- Adams and D. Smith, J. Phys. B 9 (1976) 1439. V.G. Anicich, J.B. Laudenslager znd W.T. Hunfress Jr., J. Chem. Phys. 67 (1977) 4340. J-B. JI.audens!dager, M-T. Boaiea and W-T. Huntress Jr., J. Chem. Phys 61(1974) 4600. V. Aquilanti, A- Galli, k GriordiniGuidoni and G.G. Volpi, J. Chem. Phys. 43 (1965) 1969. D-L Albritton, M. McFarland and A.J-..Schmeltekopf, J. Chem. Phys. 58 (1973) 4036. RC Bolden, RS. Hemsworth, M.J. Shaw and N.D. Twiddy, 3. Phys. B 3 (1970) 45.
[ll
15 January 1979
] N-G. Adams,A.G. Dean and D. Smith, Intern- J. Mass
Spectrom. Ion Phys. 10 (1972) 63. T.F. Moran and L Friedrn~, J. Chem. Phys 45 (1966) 3837. [I31 R.C Bolden and N.D. Twiddy, Faraday Discussions them. Sot. 53 (1972) 192. (141 C-J. Howard, H.W. R-undeB and F. Kaufman. J. Chem. Phys. 53 (1970) 3745. [IS] UT. Bower and D.D. EIIeman, Chem. Phys Letters 16 (1972) 482. [ 161 E.G. Jones and A.G. Harrison, Intern. J. Mass Speceom. Ion Phys. 6 (1971) 77. j12]