Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6323, USA.
J Chem Phys. 2018 Jun 28;148(24):244305. doi: 10.1063/1.5037164.
We developed the mixed quantum/classical theory (MQCT) for rotationally and vibrationally inelastic scattering of a diatomic molecule in a Σ electronic state with a closed-shell atom. In this approach, the rotational (and vibrational) fine-structure states of the molecule are treated quantum-mechanically, whereas the relative motion of collisional partners is treated classically. This theory is benchmarked against full quantum (close-coupling) calculations for the NH(XΣ) + He system. Good agreement is found in all cases, and MQCT reproduces all main features of energy dependence of the cross section, except narrow scattering resonances at very low energies. Our method recovers propensity rules that govern values of close-coupling cross sections. Particularly, MQCT correctly predicts that the magnitudes of F-conserving transitions are significantly larger than those of F-changing ones. This new development makes MQCT a viable candidate for obtaining fine-structure resolved rotational rate coefficients at higher temperatures and for complex polyatomic systems where the standard full quantum treatment is computationally infeasible.
我们开发了一种用于Σ电子态双原子分子与闭壳原子之间的旋转和振动非弹性散射的混合量子/经典理论（MQCT）。在这种方法中，分子的旋转（和振动）精细结构态以量子力学方式处理，而碰撞伙伴的相对运动则以经典方式处理。该理论与 NH(XΣ) + He 体系的全量子（紧密耦合）计算进行了基准测试。在所有情况下都发现了良好的一致性，并且 MQCT 再现了截面能量依赖性的所有主要特征，除了非常低能量下的狭窄散射共振。我们的方法恢复了支配紧密耦合截面值的倾向性规则。特别地，MQCT 正确地预测了 F 守恒跃迁的幅度明显大于 F 改变跃迁的幅度。这一新发展使 MQCT 成为在更高温度下获得精细结构分辨旋转速率系数以及在标准全量子处理计算上不可行的复杂多原子体系中的可行候选者。
