Study of the recombination reaction CH/sub 3/ + CH/sub 3/. -->. C/sub 2/H/sub 6/. 2. Theory
Journal Article
·
· J. Phys. Chem.; (United States)
A microcanonical variational RRKM rate constant calculation, based on the flexible transition-state theory of Wardlaw and Marcus (Chem. Phys. Lett. 1984, 110, 230) and an adjustable semiempirical potential energy surface, is compared to the measurement of part 1 (preceding paper in this issue) and other experimental studies. The calculations contain two adjustable parameters: a potential parameter ..cap alpha.., which influences the tightness of the transition state, and <..delta..E>/sub tot/, the total average energy change in metastable C/sub 2/H/sub 6/* per collision with the buffer gas. When the parameters are optimized, the resulting calculated rate constants have a 9.9% root mean square error with respect to the measurements in Ar buffer gas. The final parameter values are ..cap alpha.. = 0.70 +/- 0.13 A/sup -1/ and <..delta..E>/sub tot/ = -205 +/- 65 cm/sup -1/. Similar calculations for He buffer gas produce 22.4% error when compared to the less extensive measurements and give an optimized <..delta..E>/sub tot/ value of about -135 cm/sup -1/. The rate calculations for Ar buffer gas have been extended to 2000 K and then fit over the full temperature and pressure range to a modification of the functional form of Gilbert et al. (Ber. Bunsen-Ges. Phys. Chem. 1983, 87, 161). The resulting fitted functions required by that form are k/sub 0/ = 8.76 x 10/sup -7/T/sup -7.03/e/sup -1390/T/(Ar) cm/sup 3//(molecule s), F/sub cent/ = 0.381e/sup -T/73.2/ + 0.619e/sup -T/1180/, and k/sub infinity/ = 1.50 x 10/sup -7/T/sup 1.18/e/sup -329/T/ cm/sup 3//(molecule s). When used in the Gilbert et al. function, this parametrization produces an excellent representation of the theoretical and experimental rate constants in Ar.
- Research Organization:
- Argonne National Lab., IL (USA)
- DOE Contract Number:
- W-31109-ENG-38
- OSTI ID:
- 7143904
- Journal Information:
- J. Phys. Chem.; (United States), Journal Name: J. Phys. Chem.; (United States) Vol. 92:9; ISSN JPCHA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
ALKANES
ALKYL RADICALS
CHEMICAL REACTION KINETICS
DATA
ENERGY TRANSFER
ETHANE
HYDROCARBONS
INFORMATION
KINETICS
METHYL RADICALS
NUMERICAL DATA
ORGANIC COMPOUNDS
POTENTIALS
RADICALS
REACTION KINETICS
RECOMBINATION
THEORETICAL DATA
400201* -- Chemical & Physicochemical Properties
ALKANES
ALKYL RADICALS
CHEMICAL REACTION KINETICS
DATA
ENERGY TRANSFER
ETHANE
HYDROCARBONS
INFORMATION
KINETICS
METHYL RADICALS
NUMERICAL DATA
ORGANIC COMPOUNDS
POTENTIALS
RADICALS
REACTION KINETICS
RECOMBINATION
THEORETICAL DATA