MICROWAVE-SPECTRUM AND STRUCTURE OF TRIMETHYLPHOSPHINE SELENIDE

The microwave spectra of (CH3)(3) P-82 Se, (CH3)(3)p(80) Se, (CH3)(3)p (78) Se and (CH3)(3) p(76) Se from 26.5 to 39.0 GHz have been measured at ambient temperature and the observed transitions have been assigne d for the ground vibrational states for each isotope. With an assumed carbon-hydrogen distance of 1.090 Angstrom the following r(0) structur al parameters have been determined: r(P=Se) = 2.091 +/- 0.017 Angstrom ; r(P-C) = 1.817 +/- 0.006 Angstrom; angle CPSe = 113.8 +/- 0.9 degree s; and angle HCP = 110.1 +/- 1.9 degrees. The bond length for the P=Se bond lies close to the value expected for a double bond and it is in agreement with the previously reported value for this bond from an ele ctron diffraction study. Ab initio calculations with the STO-3G basis set have been carried out and compared with the experimental values.