The CH 3POF 2 molecule: ab initio studies of structure, vibrational spectrum and methyl rotational barrier

Abstract

The molecular structure and vibrational spectrum of methylphosphonic difluoride (CH 3POF 2) were determined through ab initio calculations at HF, MP2 and DFT/B3LYP levels using several gaussian basis sets. For the first time, electronic correlation methods were used to obtain molecular properties in this system. The results were compared with previous theoretical and experimental studies. The addition of two sets of d-type polarization functions on heavy atoms is necessary in order to reproduce the experimental dipole moment and vibrational frequencies. The use of a good quality basis set also provided a great improvement in the description of the normal modes of vibration: the mixing between PO stretching and CH 3 symmetric deformation was correctly predicted for the first time. Methyl rotation was followed by means of an intrinsic reaction coordinate calculation at MP2/6-31G(2d,p) level. The corresponding rotational barrier is 1.49 kcal/mol.