Isomerization and dissociation in competition: The two-component dissociation rates of methyl propionate ions
- Univ. of North Carolina, Chapel Hill, NC (United States). Chemistry Dept.
Threshold photoelectron-photoion coincidence (TPEPICO) spectroscopy has been used to investigate the unimolecular chemistry of gas-phase methyl propionate ions. This ion undergoes isomerization to a lower energy enol structure, CH{sub 3}CHC(OH)OCH{sub 3}{sup {sm_bullet}+}, via two different pathways involving two distonic isomers, {sup {sm_bullet}}CH{sub 2}CH{sub 2}C{sup +}(OH)OCH{sub 3} and CH{sub 3}CH{sub 2}C{sup +}(OH)OCH{sub 2}{sup {sm_bullet}}. This isomerization reaction is in competition with the direct CH{sub 3}O{sup {sm_bullet}} loss reaction, which leads to two-component dissociation rates of the methyl propionate ions. Detailed modeling of this complex reaction permitted the extraction of the dissociative photoionization threshold for methyl propionate, which at 0 K is 10.83 {+-} 0.01 eV, as well as the isomerization barrier between the distonic CH{sub 3}CH{sub 2}C{sup +}(OH)OCH{sub 2}{sup {sm_bullet}} and enol CH{sub 3}CHC(OH)OCH{sub 3}{sup {sm_bullet}+} ions of 8.5 kcal/mol (relative to the methyl propionate ion). By combining this with the 0 K heats of formation of methyl propionate and the methoxy radical, the authors derive a 0 K heat of formation of the product propanoyl ion of 147 kcal/mol. Also measured was the adiabatic ionization energy of methyl propionate, 10.03 {+-} 0.05 eV.
- Sponsoring Organization:
- USDOE, Washington, DC (United States)
- OSTI ID:
- 349882
- Journal Information:
- Journal of Physical Chemistry A: Molecules, Spectroscopy, Kinetics, Environment, amp General Theory, Journal Name: Journal of Physical Chemistry A: Molecules, Spectroscopy, Kinetics, Environment, amp General Theory Journal Issue: 9 Vol. 103; ISSN 1089-5639; ISSN JPCAFH
- Country of Publication:
- United States
- Language:
- English
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