Department of Chemistry, New York University, New York, New York 10003, USA.
J Chem Phys. 2013 Jun 28;138(24):244707. doi: 10.1063/1.4811220.
We report rigorous quantum five-dimensional (5D) calculations of the coupled translation-rotation (TR) energy levels and wave functions of an H2 molecule, in the ground (ν = 0) and vibrationally excited (ν = 1) states, confined inside the octahedral interstitial site of solid C60 with S6 symmetry. Translational and rotational excitations of H2 in this nanocavity have been measured by the inelastic neutron scattering (INS) and infrared (IR) spectroscopy, enabling direct comparison between theory and experiment. A pairwise additive 5D intermolecular potential energy surface (PES) was employed in the calculations. The quantum calculations cover the range of energies and types of translational and rotational excitations of the guest molecule which go substantially beyond those considered in the earlier theoretical investigations of this system, revealing new information about the TR energy level structure. The computed j = 1 and j = 2 rotational levels and their splittings, as well as the translational fundamental, are in semi-quantitative agreement with the available INS and IR data, indicating the need for a more accurate intermolecular PES. Our calculations reveal a strong dependence of the TR energy levels, in particular their splittings, on the setting angle which defines the orientation of the C60 molecules relative to their local threefold axes.
我们报告了严格的量子五维（5D）计算，计算了处于基态（ν=0）和振动激发态（ν=1）的 H2 分子的耦合平移-旋转（TR）能级和波函数，该分子被限制在具有 S6 对称性的固体 C60 的八面体间隙位点内。H2 在这个纳米腔中的平移和旋转激发已通过非弹性中子散射（INS）和红外（IR）光谱进行了测量，这使得理论和实验之间可以直接进行比较。在计算中采用了双体加和的 5D 分子间势能面（PES）。量子计算涵盖了访客分子的平移和旋转激发的能量范围和类型，这些范围大大超过了该系统早期理论研究中考虑的范围，揭示了有关 TR 能级结构的新信息。计算出的 j=1 和 j=2 旋转能级及其分裂以及平移基态与可用的 INS 和 IR 数据在半定量上是一致的，这表明需要更准确的分子间 PES。我们的计算表明，TR 能级，特别是它们的分裂，强烈依赖于定义 C60 分子相对于其局部三倍轴的取向的设置角。
