Ab initio studies of the homodimers of methane and silane - Geometries, interaction energies and vibrational spectra

The structures and vibrational spectra of the weakly bound homodimers of methane and silane have been determined by means of a series of ab initio calculations at the level of second order Møller-Plesset perturbation theory and with a triple-zeta split valence Gaussian basis set augmented with polarization and diffuse functions on all atoms. The similarities and differences in the properties have been rationalized largely on the basis of the differing molecular quadrupole moments and polarizabilities, and the polarities of the CH and SiH bonds. The computed vibrational spectrum of the methane dimer has been compared with some literature infrared and Raman spectra measured in cryogenic matrices.