Conformational stability from temperature-dependent FT-IR spectra of xenon solutions and ab initio calculations for ethyldichlorophosphine

Abstract

The mid-infrared spectra (3100 to 400 cm −1) of ethyldichlorophosphine dissolved in liquid xenon as a function of temperature (−60 to −100°C) have been recorded. Using the conformer pairs ( gauche/trans) observed at 1024 1041 , 751 726 , and 665 632 cm −1 , the enthalpy difference has been determined to be 79 ± 14 cm −1 (226 ± 41 cal mol −1) with the trans conformer being more stable than the high energy gauche form. The optimized geometries, conformational stabilities, harmonic force fields, infrared intensities, Raman activities, depolarization ratios, and vibrational frequencies are reported for both conformers from RHF 3-21 G∗ , RHF 6-31 G∗ , and MP2 6-31 G∗ ab initio calculations. The ab initio calculations predict the gauche conformer to be more stable which is at variance with the experimental results. The other theoretical results are compared to the experimentally determined values where applicable and with corresponding results obtained for some similar molecules.