Theoretical Reaction Dynamics Study of the Effect of Vibrational Excitation of CO on the OH + CO → H + CO2 Reaction

Abstract

The OH + CO → H + CO2 reaction has received a great deal of attention in recent years, being presently the prototypical complex-forming four-atom reaction. An interesting issue is the extent to which the vibration of the nonreactive CO bond acts as a spectator in the reaction. To get insight into this question, we report a study of the reactivity of the ground (ν = 0, j = 0) and first excited vibrational state (ν = 1, j = 0) of CO with the OH diatom in its ground rovibrational state (ν = 0, j = 0). For these reactions, the time-dependent wave packet (TDWP) method was used to calculate exact, full-dimensional (6D) initial-state selected reaction probabilities on the Bradley-Schatz potential energy surface (PES), for total angular momentum J = 0. An approximate diabatic (potential-averaged five-dimensional, PA5D) model was also used, in which the 6D potential is averaged over one asymptotic CO vibrational wave function. The results show a large increase in reactivity upon vibrational excitation of CO, particularly in the 6D model. A comparison of the 6D results with the diabatic PA5D results for CO (ν = 1), as well as the analysis of the potential curves constructed according to an adiabatic 5 + 1D model, reveal that this effect is mostly due to vibrationally inelastic energy transfer from the CO bond to the reaction coordinate. The reactivity of CO (v = 1) is much higher in the 6D than in the PA5D model. These findings allow us to conclude that the CO bond does not act as a spectator in the reaction. Finally, the quasiclassical trajectory (QCT) method was employed on the above-mentioned Bradley-Schatz PES, as well as on the most recent PES (LTSH). The QCT method is able to predict quite well the difference between the 6D and PA5D reaction probabilities for CO (ν = 1) obtained with the TDWP method on the BS PES. The PA5D QCT results are also in good agreement with 6D and PA5D TDWP results for reaction of CO (ν = 0) and for the BS PES. The large differences found between QCT reaction probabilities for CO (ν = 1) in the 6D and the PA5D model, on one hand, and the large differences between 6D QCT results for CO (ν = 1) and PA5D QCT results for CO (ν = 0), on the other hand, for the LTSH PES, strongly suggest that our conclusion (CO does not act as a spectator) can be generalized to this newer PES.