D+CD_4→CD_3+D_2反应的四维量子散射计算

Four-dimensional quantum scattering calculations on the D+CD_ 4→CD_ 3+D_ 2 reaction

运用约化维数量子动力学理论 ,利用含时波包法 ,对反应D +CD4 →CD3+D2 进行了四维量子散射计算 .将反应多原子CD4 看作双原子D—CD3,反应D +CD4 →CD3+D2 看作单原子 双原子反应 ,把体系的反应简化为四维散射问题 .波函数的传播采用分裂算符法 ,为避免格点边界处含时波函数的边界反射 ,采用了光学吸收势法 ,在格点边界处引入光学势 ,消除边界反射 .根据CD4 分子的C3v对称性 ,选取了Jordan和Gilbert提出的半经验势能面 .计算结果表明 ,反应概率随平动能的变化图像 ,呈现出显著的量子共振特性 ,这是很多提取反应的共同特征 .而不同振动态下的反应概率随平动能的变化表明 ,随振动量子数的增大 ,反应概率有明显提高 ,且反应阈能明显降低 ,这说明反应分子的振动能对分子的碰撞反应有重要贡献 .而对基态和第一振动激发态时散射截面的计算 ,也证明了这一结论 .同时 ,还分别通过计算量子数j,k ,m对反应概率的影响 ,对该反应的空间取向效应进行了研究 ,并与H +CH4→CH3+H2 反应进行了比较 .

The dynamics for the D+CD 4→CD 3+D 2reaction have been studied using reduced dimensionality quantum-mechanical theory. By the theory, the reactive polyatomic molecule CD 4was treated as a diatomic molecule D—CD 3, so the system can be treated as a linear atom-diatom reaction, reducing the system to a four-dimensional scattering problem. In calculations, the Hamiltonian of the reaction system has been carried out using the time-dependent wave packet method, and the propagation of wave packets by the split-operator method. The semiempirical potential energy surface which has been developed by Jordan and Gilbert is employed. The energy dependence of the calculated reaction probability shows oscillatory structures, similar to those observed in abstraction reactions H+H 2, H+CH 4,etc. The excitation of the stretching vibration of reactive molecule D—CD 3gives a significant enhancement of reaction probability, the reaction threshold decreases with the enhancement of the vibrating excitation. Detailed study of the influence of initial rotational states on reaction probability shows a strong steric effect. The integral cross sections of translational energy for CD 4at both v=0 and v=1 at ground rotational state show that the vibrational excitation significantly enhances the reaction cross section. And the reaction threshold decreases by about 0.2eV, consistent with that of reaction probability. The significant enhancement of the reaction probability of reaction H+CH 4at ground state when compared with D+CD 4 can be explained reasonably in terms of quantum mechanical zero-point energies and the tunneling effect.