Quasiclassical trajectory calculations of correlated product distributions for the F+CHD_3(v1=0,1) reactions using an ab initio potential energy surface

摘要

We report quasiclassical trajectory (QCT) calculations of the correlated product distributions and branching ratios of the reactions F+CHD_3(v_1=0,1)→HF(v)+CD_3(v) and DF(v)+CHD_2(v) using a recently published ab initio-based full-dimensional global potential energy surface [G. Czako et al., J. Chem. Phys. 130, 084301 (2009)]. Harmonic normal mode analysis is done for the methyl products to determine the classical actions of each normal mode and then standard histogram binning and Gaussian binning (GB) methods are employed to obtain quantum state-resolved probabilities of the products. QCT calculations have been performed for both the vibrationally ground state and the CH stretching excited F+CHD_3(v_1=0,1) reactions at eight different collision energies in the 0.5–7.0 kcal/mol range. HF and DF vibrationally state-resolved rotational and angular distributions, CD_3 and CHD_2 mode-specific vibrational distributions, and correlated vibrationally state-specific distributions for the product pairs have been obtained and the correlated results were compared to the experiment.We find that the use of GB can be advantageous especially in the threshold regions. The CH stretching excitation in the reactant does not change the CD_3 vibrational distributions significantly, whereas the HF molecules become vibrationally and rotationally hotter. On the other hand in the case of the DF+CHD_2 channel the initially excited CH stretch appears mainly “intact” in the CHD_2 product and the DF distributions are virtually the same as formed from the ground state CHD_3 reaction. The computed results qualitatively agree with recent crossed molecular beam experiment [W. Zhang et al., Science 325, 303 (2009)] that (a) CHD_2(v_1=1) is the most populated product state of the F+CHD_3(v_1=1) reaction and this reaction produces much less CHD_2(v=0) compared to the reaction F+CHD_3(v=0); (b) the cross section ratio of CHD_2(v_1=1) :CHD_2(v=0) formed from the reactions F+CHD_3(v_1=1):F+CHD_3(v=0) is less than 1 and shows little collision energy dependency; (c) the reactant CH stretch excitation increases the DF:HF ratio at low collision energies; (d) the correlated vibrational and angular distributions for DF(v)+CHD_2(v_1=0,1) from the ground state and stretch-excited reactions, respectively, are almost identical.