Quasiclassical trajectory calculations analyzing the role of vibrational and translational energy in the F+CH2D2 reaction

Abstract

An exhaustive state-to-state dynamics study was performed to analyze the effects of vibrational excitation and translational energy on the dynamics of the F + CH(2)D(2) gas-phase reaction, which are connected to such issues as bond selectivity, mode selectivity, and Polanyi's rules. This reaction can evolve along two channels: D-abstraction, DF(v(')) + CH(2)D(v(')), and H-abstraction, HF(v(')) + CHD(2)(v(')). Quasiclassical trajectory calculations were performed on an analytical potential energy surface previously developed by our group. Vibrational excitation of the C-D or C-H mode of CH(2)D(2) favors slightly the D-abstraction over the H-abstraction, indicating that this reaction does not exhibit bond selectivity and suggesting a breakdown of the spectator model. For D-abstraction, the vibrational excitation of the nonreactive C-H stretch mode is partially retained in the products, and for H-abstraction, the excitation of the nonreactive C-D stretch mode is also partially retained in the products, indicating that this reaction exhibits mode selectivity only partially. Moreover, the independent excitation of the C-H symmetric or asymmetric stretch modes leads to reactions with similar (practically identical) reaction cross sections and product scattering distributions, discarding bond selectivity and mode selectivity for this reaction. Finally, for this "early transition state" reaction, vibrational energy is more effective in driving the reaction than an equivalent amount of energy in translation, indicating that the application of the Polanyi rules that are well established in atom-diatom reactions is neither straightforward nor always valid in polyatomic reactions. All these results were interpreted on the basis of strong coupling between modes along the reaction path, a behavior which seems to be more of the general tendency than the exception in polyatomic reactions.