Dissociation of 1,1,1-trifluoroethane is an intrinsic RRKM process: classical trajectories and successful master equation modeling.

Abstract

Rate constants for thermal decomposition of 1,1,1-trifluoroethane (CH3CF3) in the high-temperature falloff region were previously reported to have an unusual pressure dependence that could not be explained by Rice-Ramsperger-Kassel-Marcus (RRKM) theory in combination with unimolecular master equation analysis. This study investigates the dynamics of the CH3CF3 dissociation and the energy transfer of CH3CF3 in collisions with Ar and Kr by classical trajectory calculations on a global potential energy surface constructed from a large number of quantum chemical calculations. The simulations showed that the ensemble-averaged CH3CF3 populations decay with single exponential profiles that have rate constants close to those predicted by RRKM theory, indicating that the microcanonical ensemble is maintained during decomposition. The trajectory calculation also indicated that a significant portion of the HF product is formed in its vibrationally excited state. Such observation motivated this study to correct some of the reported rate constants for the CH3CF3 decomposition. With the correction applied, the experimental rate constants were well reproduced by the RRKM/master equation calculation using the collisional energy transfer parameters that were also obtained from trajectory calculations. Overall, the title reaction is demonstrated to be another successful example of RRKM/master equation modeling.