An ab initio and density functional theory study of the structure and vibrational frequencies of the CH_2FO centre dot and CHF_2O centre dot radicals

摘要

Atmospheric degradation of fluorinated ether compounds, which are being considered ad replacements for the current generation of freon substituents, and is expected to produce the CH_2FO centre dot and CHF_2O centre dot radicals, and the latter radical is believed to be formed in the course of flame suppression by halons. In the present study, the molecular structures of the two radicals are determined using one density functional and two correlated ab initio methods. Structures were determined using Becke's three-parameter exchange functional with non-local correlation from the Lee, Yang, and Parr functional (the B3LYP functional) and second order unrestricted Moller-Plesset (UMP2) theory. Basis sets ranging from 631G(d) to 6311G(3df,2pd) were employed. The quadratic configuration interaction method with singles, doubles, and a perturbative treatment of the triples excitations (QCISD(T)) was employed at a more restricted range of basis sets. The C-O bond length is somewhat sensitive to the level of theory employed but somewhat less dependent on the basis set employed. Comparison is made to structural features of the CH_3O centre dot and CH_3O centre dot radicals. Vibrational frequencies were determined at B3LYP for basis sets up to 6-311G(2df,2p).