The quantitative prediction and interpretation of the vibrational spectra of organophosphorus compounds: Part II. Methylphosphonic difluoride CH 3(PO)F 2, methylphosphonothioic difluoride CH 3(PS)F 2 and methylphosphonofluoridic acid CH 3(PO)FOH

Abstract

The results of ab initio SCF MO calculations made using the 3-21G* and 6-31G* basis sets for three related methylphosphono difluoride compounds are presented. The optimized geometries from these calculations are compared with the experimental bond distances and bond angles obtained from studies of their microwave spectra. The vibrational spectra [frequencies and infrared (IR) intensities] for these three molecules have been calculated using the 3-21G* basis set. The predicted spectra have been compared with the experimental IR spectra of the molecules in the gas phase. The calculated potential-energy distributions provide a basis for assigning the experimental spectra, which is in general agreement with the assignment made previously on the basis of spectra of model compounds and characteristic frequencies. In a few cases the calculations suggest some minor adjustments to the previous assignment. The agreement between the previous assignment and that based on the calculations for CH 3(PO)F 2 and for CH 3(PS)F 2 provides support for our assignment of the IR spectrum of CH 3(PO)F(OH). The intensity sums are examined, and the calculated values of the “mass-weighted squared effective charges” (one of the invariants of the atomic polar tensors) for all the atoms in all of these molecules are presented.