The spin-forbidden reaction CH({sup 2}{Pi})+N{sub 2}{r_arrow}HCN+N({sup 4}S) revisited. II. Nonadiabatic transition state theory and application

Journal Article · Sat May 01 04:00:00 EDT 1999 · Journal of Chemical Physics

DOI:https://doi.org/10.1063/1.478949· OSTI ID:337508

Cui, Q; Morokuma, K; Bowman, J M ^[1]; Klippenstein, S J ^[2]

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1. Cherry L. Emerson Center for Scientific Computation and Department of Chemistry, Emory University, Atlanta, Georgia 30322 (United States)
2. Department of Chemistry, Case Western Reserve University, Cleveland, Ohio 44106-7078 (United States)

Transition state theory is extended straightforwardly to treat nonadiabatic processes and applied to study the rate constant of the spin-forbidden reaction CH({sup 2}{Pi})+N{sub 2}{r_arrow}HCN+N({sup 4}S). A one-dimensional model was set up to calculate the intersystem crossing probability with the distorted wave approximation and using an {ital ab initio} value of the spin{endash}orbit coupling. The effect of orthogonal degrees of freedom was then considered by energy convolution with the vibrational frequencies, obtained from {ital ab initio} calculations, orthogonal to the crossing seam at the minimum of the seam of crossing (MSX), also obtained from {ital ab initio} calculations. An expression for the cumulative reaction probability, N(E), of the reaction was obtained by a straightforward extension of the unified statistical theory, where the MSX was treated as a transition state. The calculated thermal rate constant, k(T), seems to be too low by two orders of magnitude compared to experimental measurements and an empirical transition state study where {ital empirical} vibrational frequencies at the MSX are lower by a factor of 2 than those derived here. The disagreement strongly suggests that the current treatment of the multidimensional dynamics needs to be improved. In particular, it may be a poor assumption that spin-forbidden transition takes place with uniform probability on the seam in the case we are considering. {copyright} {ital 1999 American Institute of Physics.} thinsp

• OSTI ID: 337508
• Journal Information: Journal of Chemical Physics, Journal Name: Journal of Chemical Physics Journal Issue: 19 Vol. 110; ISSN JCPSA6; ISSN 0021-9606
• Country of Publication: United States
• Language: English

Related Subjects

40 CHEMISTRY
CHEMICAL REACTION KINETICS
COMBUSTION
COMBUSTION KINETICS
FORBIDDEN TRANSITIONS
METHYLENE RADICALS
NITROGEN
ORGANIC COMPOUNDS
QUANTUM MECHANICS
SPIN
VIBRATIONAL STATES