反应物分子初始振动激发对H+CH~+→C~++H_2反应的影响

在CH_2~+体系的电子基态势能面上运用准经典轨线方法,研究了当碰撞能E=500 me V时,反应物分子的振动激发对H(~2S)+CH~+(X~1Σ~+)→C+(~2P)+H_2(X1_gΣ~+)反应的反应概率、反应截面和立体动力学性质的影响.分别计算了两矢量相关k-j′的P(θ_r)分布,三矢量相关k-k′-j′的P(φr)分布以及反应产物的四个极化微分截面.结果表明,产物分子转动角动量不仅在Y轴方向有取向效应,还定于Y轴的正方向.并且发现,随着振动量子数的增加,对反应体系产物分布的影响就越明显.

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

The effect of reagent vibrational excitation on the stereodynamical properties of H(²S)+CH⁺(X¹Σ⁺)→C⁺(²P)+H₂(X¹Σ_g⁺)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(θ_r), the dihedral angle distribution P(φ_r), and the polarization-dependent generalized differential cross sections are calculated. P(θ_r) represents the relation between the reagent relative velocity k and the product rotational angular momentum j'. P(φ_r) describes the correlation of k-k'-j', in which k' is the product reagent relative velocity. The peak of P(θ_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(θ_r) distribution becomes increasingly obvious with the increase of the rotational quantum number. The dihedral angle distribution P(φ_r) tends to be asymmetric with respect to the k-k' scattering plane (or about φ_r= 180°), directly reflecting the strong polarization of the product angular momentum for the title reaction. Each curve has two evident peaks at about φ_r = 90° and φ_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 φ_r= 90° is apparently stronger than that at φ_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 θ_r and φ_r. The distribution of P(θ_r; φ_r) is well consistent with the distribution P(θ_r) and also the distribution P(φ_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.