Abstract: Various possible structures of the CH₃F dimer have been optimized at the MP2/6-311+ +G(3d,3p) electron correction level, three minimum geometrical structures have been found on the potential energy surface. At a high order electron correction MP4SDTQ and CCSD(T)/6-311+ +G(3df,3pd) level, the binding energy of the most stable structure which is planar cyclic C_2h symmetry of the dimer has been calculated exactly and the binding energy ΔE_CPCCSD(T) is -9.707 kJ/mol. The calculated results of the harmonic vibrational frequencies of three minimum geometries support the structures guessed by the spectra experiment. Diversity of the harmonic vibrational frequency has been explained.

Key words: CH₃F, Intermolecular interaction, Bind energy, Ab initio