A study of the dissociation of CH{sub 3}CH{sub 2}SH{sup +} by collisional activation: Evidence of nonstatistical behavior
- Ames Laboratory, United States Department of Energy, Ames, Iowa and Department of Chemistry, Iowa State University, Ames, Iowa50011 (United States)
- Department of Chemistry, The Chinese University of Hong Kong, Shatin, N. T. (Hong Kong)
- Department of Applied Biology and Chemical Technology, Hong Kong Polytechnic University, Hung Ham (Hong Kong)
The absolute total cross sections for CH{sub 3}CH{sub 2}{sup +}, C{sub 2}H{sub 4}{sup +}, C{sub 2}H{sub 3}{sup +}, CH{sub 3}{sup +}, CH{sub 2}SH{sup +}(CH{sub 3}S{sup +}), CH{sub 2}S{sup +}(HCSH{sup +}), CHS{sup +}(CSH{sup +}), and H{sub 2}S{sup +} produced by the collision-induced dissociation (CID) reaction of CH{sub 3}CH{sub 2}SH{sup +}+Ar have been measured in the center-of-mass collision energy (E{sub c.m.}) range of 1{endash}42 eV. Using the charge transfer probing technique, we found that the mass 47 product ions have overwhelmingly the CH{sub 2}SH{sup +} structure. The onsets for CH{sub 3}CH{sub 2}{sup +}, C{sub 2}H{sub 4}{sup +}, C{sub 2}H{sub 3}{sup +}, CH{sub 2}SH{sup +}, H{sub 2}S{sup +}, and CH{sub 3}{sup +} are consistent with their corresponding thermochemical thresholds. The formation of the higher energy channels CH{sub 3}CH{sub 2}{sup +}+SH and CH{sub 3}+CH{sub 2}SH{sup +}, which involve the C{endash}S and C{endash}C bond scissions, are found to dominate in the entire E{sub c.m.} range. The lower energy channel corresponding to the formation of CH{sub 3}CHSH{sup +}+H is not found. The strong preference observed for the formation of the higher energy channels is in accord with the conclusion obtained in the recent CID study of CH{sub 3}SH{sup +}, providing evidence that the CID of CH{sub 3}CH{sub 2}SH{sup +} is also nonstatistical. The high yields of CH{sub 3}CH{sub 2}{sup +}+SH and CH{sub 2}SH{sup +}+CH{sub 3} are attributed to the more efficient translational to vibrational energy transfer for the low frequencies C{endash}S and C{endash}C stretching modes than for the high frequencies C{endash}H and S{endash}H stretching modes, along with the weak couplings between these low and high frequencies vibrational modes of CH{sub 3}CH{sub 2}SH{sup +}. The relative abundances of product ions formed by the single-photon ionization of CH{sub 3}CH{sub 2}SH were also measured for comparison with the CID results. The CH{sub 3}CHSH{sup +}+H channel is observed in the photoionization of CH{sub 3}CH{sub 2}SH. Similar to the finding in the photoionization of CH{sub 3}SH, the relative abundances of fragment ions formed in the photoionization of CH{sub 3}CH{sub 2}SH are in qualitative accord with statistical predictions. To rationalize the dissociation mechanisms of CH{sub 3}CH{sub 2}SH{sup +}, we have also performed {ital ab initio} calculations to locate the possible transition structures for the observed dissociation channels. {copyright} {ital 1998 American Institute of Physics.}
- OSTI ID:
- 627748
- Journal Information:
- Journal of Chemical Physics, Journal Name: Journal of Chemical Physics Journal Issue: 19 Vol. 108; ISSN JCPSA6; ISSN 0021-9606
- Country of Publication:
- United States
- Language:
- English
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