Calculation of anharmonic effects for the unimolecular dissociation of CH3OOH and its deuterated species CD3OOD using the Rice-Ramsperger-Kassel-Marcus theory

Abstract

Anharmonic and harmonic rate constants for the unimolecular dissociation of CH3OOH and CD3OOD were calculated using the Rice-Ramsperger-Kassel-Marcus (RRKM) theory at the MP2/6-311++G(3df,3pd) level of theory. The anharmonic effect of the reactions was investigated. Comparison of results for the decompositions of CH3OOH and CD3OOD shows that the direct bond dissociation channel, CH3 (D-3) O + OH (D), is the most dominant reaction. The anharmonic effect plays an important role in the unimolecular dissociation of both CH3OOH and CD3OOD. For channels CH3 (D-3) O + OH (D) and CH3 (D-3) + H (D) O-2, the anharmonic effect of the unimolecular dissociation of CD3OOD is more pronounced than that of the unimolecular dissociation of CH3OOH. For channel H-2 (D-2) CO + H-2 (D-2) O, the anharmonic effect of the unimolecular dissociation of CH3OOH is more pronounced than that of the unimolecular dissociation of CD3OOD. The isotope effect is more distinct in the anharmonic oscillator model.