中文摘要：

本文针对煤层气中甲烷分子间作用是否影响煤层气吸附的问题，采用量子化学方法，在MP2／6—311G＋＋（3af，3pd）电子相关校正水平上，对cH4二聚体可能存在的十二种几何构型进行全自由度能量梯度优化和频率验证，对两种较稳定构型进行了基组叠加误差校正，并对这两种构型进行了振动频率和电荷分析，求得甲烷二聚体的离解能为1．81kJ·mol^-1，从而说明甲烷二聚体是弱结合分子，由此本文为煤层气吸附理论的完善提供了一定的理论依据。

英文摘要：

To find out the effect of intermolecular interaction between CH4 molecules on adsorption of CBM by coal, 12 possible structures of the （CH4）2 dimers have been optimized at the MP2/6-311 ＋ ＋ G （3df, 3pd） electron correction level by using the quantum method, and two minimum geometrical structures have been found on the potential energy surface. The intermolecular interaction energies of the two minimum geometrical structures have been corrected further by the basis set superposition error （BSSE）. The vibration frequencies and atomic charges of the two minimum geometrical structures have also been analyzed in the paper. It is found that the dissociation energy of methane dimer was 1.81 kJ·mo1^-1, so （CH4）2 is a typical weakly bounded molecule. The paper also provides some theoretic foundation for coalbed methane adsorption theory.