Department of Mechanical Engineering, Keio University, Yokohama, Kanagawa 223-8522, Japan.
J Chem Phys. 2012 Jan 28;136(4):044508. doi: 10.1063/1.3677231.
Vibrational frequencies of guest molecules in clathrate hydrates reflect the molecular environment and dynamical behavior of molecules. A detailed understanding of the mechanism for the vibrational frequency changes of the guest molecules in the clathrate hydrate cages is still incomplete. In this study, molecular vibrations of methane molecules in a structure I clathrate hydrate are calculated from ab initio molecular dynamics simulation. The vibrational spectra of methane are computed by Fourier transform of autocorrelation functions, which reveal distinct separation of each vibrational mode. Calculated symmetric and asymmetric stretching vibrational frequencies of methane molecules are lower in the large cages than in the small cages (8 and 16 cm(-1) for symmetric and asymmetric stretching, respectively). These changes are closely linked with the C-H bond length. The vibrational frequencies for the bending and rocking vibrational modes nearly overlap in each of the cages.
笼形水合物中客体分子的振动频率反映了分子的环境和分子的动力学行为。对于笼形水合物笼中客体分子振动频率变化的机制，人们还没有完全了解。在这项研究中，我们通过从头算分子动力学模拟计算了结构 I 笼形水合物中甲烷分子的振动。通过自相关函数的傅里叶变换计算了甲烷的振动谱，揭示了每个振动模式的明显分离。计算得到的甲烷分子的对称和非对称伸缩振动频率在大笼中比在小笼中低（分别为 8 和 16 cm(-1)）。这些变化与 C-H 键长密切相关。在每个笼中，弯曲和摇摆振动模式的振动频率几乎重叠。
