Structures and vibrational frequencies of ethylphosphine: post-Hartree-Fock and density functional theory study

The molecular structure and conformational stability of ethylphosphine have been investigated using ab initio and density functional theory methods. The molecular geometries are optimized employing HF, MP2, BLYP and B3LYP methods implementing 6-31G* and 6-311+ + G** basis sets. From the calculations, the molecule is predicted to exist in two stable conformers with the trans (methyl group oriented trans to the lone pair on the phosphorus atom) being slightly lower in energy than the gauche rotamers. The optimized structural parameters for both conformations are compared to the structures obtained from microwave spectroscopy. Potential surfaces for both the methyl and PH2 moiety internal rotation are determined at B3LYP and MP2 levels of theory. The vibrational frequencies are computed at different levels and compared to the fundamental values. The results indicate that the scaled B3LYP frequencies reproduce the experimental values satisfactorily with the mean absolute deviation about 19.9 cm(-1). On the basis of the comparison between calculated and experimental results, assignments of fundamental modes are examined. It is conclude that at these levels of calculations, the structure, potential surface and vibrational frequencies for ethylphosphine are well determined. (C) 2002 Elsevier Science B.V. All rights reserved.