Infrared spectra prediction and potential energy surface studies of methylarsine and methylstibine

The vibrational frequencies, normal mode assignments and the internal-rotation and inversion potential energy surfaces of methylarsine and methylstibine are reported. The potential energy distribution (PED) for each frequency is found using Kim's Correspondence Rules of unified group theory and the program MOLVIB. The predominant motion of each PED is used to name the corresponding vibrational frequency. We also report the infrared spectra prediction of deuterated isotopomers. Our predicted infrared spectra show good agreement with experiment. In the potential energy surfaces of both molecules, there are three minimum energy states; and three first-order internal-rotation, six first-order inversion, and six second-order inversion transition-states. Calculations are performed at the HF, DFT/B3LYP, and MP2 levels of theory using GAUSSIAN 03 quantum chemistry code. The 6-311G** basis set is used for methylarsine and the CEP-121G basis set is used for methylstibine.