Effect of reagent vibrational excitation on reaction of H+CH+C++H2

Abstract

The effect of reagent vibrational excitation on the stereodynamical properties of H(2S)+CH+(X1+)C+(2P)+H2(X1g+)reaction is investigated by quasi-classical trajectory method on a globally smooth ab initio potential surface of the 2A' state at a collision energy of 500 meV. The reaction probability and the reaction cross-section are also studied. In the calculation, the vibrational levels of the reactant molecules are taken as v = 0, 1, 3, 5 and j = 0, respectively, where v is the vibrational quantum number and j is the rotational quantum number. The calculation results show that the reaction probability reaches a maximum when v = 1, and then decreases with the vibrational quantum number increasing. The integral cross-section decreases sharply with the increase of vibrational quantum number. The potential distribution P(r), the dihedral angle distribution P(r), and the polarization-dependent generalized differential cross sections are calculated. P(r) represents the relation between the reagent relative velocity k and the product rotational angular momentum j'. P(r) describes the correlation of k-k'-j', in which k' is the product reagent relative velocity. The peak of P(r) is at r = 90 and symmetric with respect to 90, which shows that the product rotational angular momentum vector is strongly aligned along the direction perpendicular to the relative velocity direction. The peak of P(r) distribution becomes increasingly obvious with the increase of the rotational quantum number. The dihedral angle distribution P(r) tends to be asymmetric with respect to the k-k' scattering plane (or about r= 180), directly reflecting the strong polarization of the product angular momentum for the title reaction. Each curve has two evident peaks at about r = 90 and r = 270, but the two peak intensities are obviously different, which suggests that j' is not only aligned, but also strongly orientated along the Y-axis of the center-of-mass frame. The peak at r= 90 is apparently stronger than that at r = 270, which indicates that j' tends to be oriented along the positive direction of Y-axis. In order to validate more information, we also plot the angular momentum polarization in the forms of polar plots r and r. The distribution of P(r; r) is well consistent with the distribution P(r) and also the distribution P(r) of the products at different vibrational quantum states. In addition, the polarization-dependent differential cross section is quite sensitive to the reagent vibrational excitation. Based on the obtained results, we find that the observed excess of the methylidyne cation CH+ is closely related to the reactant of vibrational excitation in interstellar chemistry.