Direct ab initio dynamics calculations of the reaction rate for the hydrogen abstraction reaction of NCO with CH4 and C2H6.

The kinetics of the hydrogen abstraction reactions NCO + CH4 (R1) and NCO + C2H6 (R2) have been studied over a wide temperature range. The minimum energy paths (MEPs) were calculated at the MP2/cc-pVDZ level and single-point calculations were refined at the G3MP2 level. The rate constants for the title reactions were calculated using canonical variational transition state theory (CVT) with small-curvature tunneling (SCT) contributions. The fitted three-parameter formulae are k1 = 2.52 × 10-22T3.46 exp(2466/T) and k2 = 9.8 × 10-22T3.2 exp(411.8/T) cm3 molecule-1 s-1 for (R1) and (R2), respectively. The calculated rate constants were found to be in good agreement with the available experimental data. Deuterium kinetic isotope effects were also investigated. Both reactions show a significant kinetic isotope effect in the low-temperature range. [ABSTRACT FROM AUTHOR]