Departamento de Química Física, Facultad de Química, Universidad Complutense, 28040 Madrid, Spain.
J Chem Phys. 2011 Oct 7;135(13):134313. doi: 10.1063/1.3644337.
Reaction probabilities as a function of total angular momentum (opacity functions) and the resulting reaction cross sections for the collision of open shell S((1)D) atoms with para-hydrogen have been calculated in the kinetic energy range 0.09-10 meV (1-120 K). The quantum mechanical hyperspherical reactive scattering method and quasi-classical trajectory and statistical quasi-classical trajectory approaches were used. Two different ab initio potential energy surfaces (PESs) have been considered. The widely used reproducing kernel Hilbert space (RKHS) PES by Ho et al. [T.-S. Ho, T. Hollebeek, H. Rabitz, S. D. Chao, R. T. Skodje, A. S. Zyubin, and A. M. Mebel, J. Chem. Phys 116, 4124 (2002)] and the recently published accurate double many-body expansion (DMBE)/complete basis set (CBS) PES by Song and Varandas [Y. Z. Song and A. J. C. Varandas, J. Chem. Phys. 130, 134317 (2009)]. The calculations at low collision energies reveal very different dynamical behaviors on the two PESs. The reactivity on the RKHS PES is found to be considerably larger than that on the DMBE/CBS PES as a result of larger reaction probabilities at low total (here also orbital) angular momentum values and to opacity functions which extend to significantly larger total angular momentum values. The observed differences have their origin in two major distinct topographic features. Although both PESs are essentially barrierless for equilibrium H-H distances, when the H-H bond is compressed the DMBE/CBS PES gives rise to a dynamical barrier which limits the reactivity of the system. This barrier is completely absent in the RHKS PES. In addition, the latter PES exhibits a van der Walls well in the entrance channel which reduces the height of the centrifugal barrier and is able to support resonances. As a result, a significant larger cross section is found on this PES, with marked oscillations attributable to shape resonances and/or to the opening of partial wave contributions. The comparison of the results on both PESs is illustrative of the wealth of the dynamics at low collision energy. It is also illuminating about the difficulties encountered in modeling an all-purpose global potential energy surface.
作为总角动量（不透明度函数）的函数的反应概率以及开放壳 S((1)D) 原子与仲氢碰撞的反应截面已在 0.09-10 meV（1-120 K）的动能范围内进行了计算。使用了量子力学的超球反应散射方法和准经典轨迹和统计准经典轨迹方法。考虑了两种不同的从头算势能面（PES）。广泛使用的 Ho 等人提出的复制核希尔伯特空间（RKHS）PES [T.-S. Ho、T. Hollebeek、H. Rabitz、S. D. Chao、R. T. Skodje、A. S. Zyubin 和 A. M. Mebel，J. Chem. Phys 116，4124（2002）]和最近发表的准确双多体展开（DMBE）/完全基集（CBS）PES Song 和 Varandas [Y. Z. Song 和 A. J. C. Varandas，J. Chem. Phys. 130，134317（2009）]。在低碰撞能下的计算揭示了两种 PES 上非常不同的动力学行为。由于在低总（这里也是轨道）角动量值下的反应概率更大，并且不透明度函数扩展到明显更大的总角动量值，因此在 RKHS PES 上的反应性发现比在 DMBE/CBS PES 上大得多。观察到的差异源于两个主要的不同地形特征。尽管对于平衡 H-H 距离，两个 PES 基本上都是无势垒的，但当 H-H 键被压缩时，DMBE/CBS PES 会产生一个动力学障碍，限制了系统的反应性。这种障碍在 RHKS PES 中完全不存在。此外，后者 PES 在入口通道中表现出范德华阱，降低了离心势垒的高度，并能够支持共振。结果，在这个 PES 上发现了一个明显更大的截面，其显著的振荡归因于形状共振和/或部分波贡献的打开。在这两个 PES 上的结果的比较说明了在低碰撞能下的动力学的丰富性。它也说明了在建模通用全局势能面时遇到的困难。
