15min:

JINPENG XIAO, JAMES B. ROBB II AND JAMES R. DURIG, Department of Chemistry, University of Missouri-Kansas City, Kansas City, MO 64110-2499, USA.

Variable temperature (-55 to -150^\circC) studies of the infrared spectra (3500 to 400 cm^-1) of ethylphosphonic difluoride, CH₃CH₂P(O)F₂ and ethylphosphonothioic difluoride, CH₃CH₂P(S)F₂ dissolved in liquid xenon or krypton have been recorded. From these data, the enthalpy differences have been determined to be 76\beginmath \pm \endmath9 cm^-1 (0.91\beginmath \pm \endmath0.11 kJ/mol), for CH₃CH₂P(O)F₂ with the trans conformer the more stable rotamer and 53\beginmath \pm \endmath7 cm^-1 (0.63\beginmath \pm \endmath0.08 kJ/mol) for CH₃CH₂P(S)F₂ but with the gauche conformer the more stable form. Complete vibrational assignments are presented for both molecules, which are consistent with the predicted frequencies obtained from the ab initio MP2/6-31G(d) calculations. The optimized geometries, conformational stabilities, harmonic force fields, infrared intensities, Raman activities, and depolarization ratios have been obtained from RHF/6-31G(d) and/or MP2/6-31G(d) ab initio calculations. These quantities are compared to the corresponding experimental quantities when appropriate as well as with some corresponding results for some similar molecules. The r_o adjusted structural parameters have been obtained for both molecules from a combination of the microwave rotational constants and ab initio predicted parameters. The corresponding r_o structural parameters have been obtained for some similar molecules for comparison.