基于量子化学计算的乙烷、乙烯、乙炔水合物主客体间相互作用特性研究

天然气水合物是一种特殊的笼状化合物，水合物中的客体分子不同，主客体间的相互作用存在差异。为了分析烃类水合物中主客体间相互作用的特征，利用量子化学方法，对乙烷、乙烯、乙炔这3种客体分子占据Ⅰ型水合物T笼时的结构、相互作用能及C—C键伸缩振动频率进行研究，讨论了客体分子在水笼中的赋存形态，揭示了主客体间的相互作用机制。结果表明：客体分子占据T笼后，与占据前相比，T笼会发生微小的膨胀或收缩，客体分子的原子间距减小；通过能量分析，发现主客体间相互作用能(ΔE_host-guest)的大小顺序为：ΔE_T笼-乙烯<ΔE_T笼-乙烷<ΔE_T笼-乙炔，色散矫正的加入使主客体间的相互作用能增大；能量分解结果显示C原子的杂化方式对水合物的主客体间相互作用影响较大，随着客体分子中C原子的杂化方式由sp³→sp²→sp杂化，客体分子与水笼间的相互作用中静电作用先略微减弱、然后增强，色散作用逐渐减弱；与未占据T笼相比，乙烷分子占据T笼后C—C键伸缩振动频率增加了6.79 cm^-1，乙烯和乙炔分子占据T笼后C—C键伸缩振动频率分别减小了5.86 cm^-1和15.87 cm^-1。

Characteristic study of the host-guest interactions in ethane,ethylene and acetylene hydrates based on quantum chemical calculation

Natural gas hydrates are cage-like compounds that can be formed with a variety of guest molecules. In order to analyze the characteristics of the interactions between the host and guest in hydrocarbon hydrates, the structure, interaction energies and C—C bond stretching vibration frequencies of ethane, ethylene and acetylene occupying the T cage of a type Ⅰ hydrate have been studied by quantum chemical calculations. The arrangement of guest molecules in the water cages is discussed, and the interactions between the host and guest are identified. The results show that, compared with before occupation, after the guest molecules occupy the T cage, it undergoes a slight expansion or contraction, and the atomic spacing of the guest molecules decreases. Through the energy analysis, it is found that the order of the interaction energy between the host and guest (ΔE_host-guest) is: ΔE_{T cage-ethylene}<ΔE_{T cage-ethane}<ΔE_{T cage-acetylene}. The addition of dispersion correction increases the calculated interaction energy between the host and guest. The energy decomposition results show that the hybridization mode of the C atoms has a major influence on the interaction between the host and guest in the hydrate. As the hybridization mode of the C atom in the guest molecule changes from sp³→sp²→sp, the electrostatic interaction between the guest molecule and the water cage initially became slightly weaker and then increased, whilst the dispersion effect gradually became weaker. The C—C bond stretching vibration frequency increased by 6.79 cm^-1 after ethane occupied the T cage, whilst the C—C bond stretching vibration frequencies decreased by 5.86 cm^-1 and 15.87 cm^-1, respectively, after ethylene and acetylene occupied the T cage.