Vibrational spectra of difluorosilane from a hybrid ab initio and DFT quartic force field

Fundamental frequencies of SiH2F2 and their isotopic shifts are computed using a hybrid quartic potential in which CCSD(T)/cc-pVTZ equilibrium values and harmonic wave-numbers are coupled to B3LYP/6-31+G** anharmonic terms in the framework of a variational treatment working in several spectral ranges. The mean-square deviation between our computed values and the most reliable experimental data are only 0.8% (SiH2F2) and 0.6% (SiD2F2). Calculation of both overtones and combination bands in the medium infrared region suggests a new assignment of some observed bands.