Influence of collision energy on the stereodynamics of the H+CH+→C++H2 reaction

Abstract

The reactive cross section and stereodynamics at selected collision energies for the H(2S)+CH+(X1Σ+)→C+(2P)+H2(X1Σg+) reaction on a globally smooth ab initio potential surface of the 2A' state are calculated in detail by the quasi-classical trajectory(QCT) method. The calculated cross section decreases with the increase of the collision energy, which is found to be in overall good agreement with the previous time-dependent quantum results in the high collision energy regime (Ec>20 meV). The discrepancy between the QCT and previous quantum cross section below 20 meV can be attributed to the limitations of the classical trajectory method, because the QCT method cannot handle the effect of zero point energy. In general, QCT results show qualitative agreement with the quantum results, which confirmsthe validity of the QCT method. The research shows that the product rotational angular momentum vector is aligned and oriented. The alignment of the product rotational angular momentum vector j' depends very sensitively on the collision energy. With the increase of the collision energy, the alignment effect recedesin the low collision energy region (1500 meV), while it is enhanced in the high collision energy region (500-1000 meV). Moreover, the k-k'-j' distributions tend to be asymmetric with respect to the k-k' scattering plane (or about φr=180°), with two peaks appearing at φr=90° and φr=270°, respectively. This indicates that the product rotational angular momentum is not only in the Y-axis direction but also along the positive Y-axis direction. The peak intensity decreases with the collision energy increasing from 1 meV to 100 meV, while it increases with collision energy increasing from 100 meV to 1000 meV. Therefore the Y-axis orientation effect turns weak with the enhancement of the collision energy in the low energy region, while it becomes strong in the high energy region. In addition, the polarization dependent differential cross sections (PDDCSs) (2π/σ)(dσ00/dωt) and (2π/σ)(dσ20/dωt) are calculated. PDDCS (2π/σ)(dσ00/dωt) results indicate that the products have almost symmetrically scattered forward and backward, and the intensity of the scattering increases with the increase of the collision energy. The PDDCS (2π/σ)(dσ20/dωt) shows that the alignment effect of the rotational angular momentum of the products is stronger at the terminal of the scattering angle than at the other directions.