Spectra and structure of organophosphorus compounds. XV. Microwave spectrum of ethylphosphine

The microwave spectra of CH3CH2PH2, CH3CH2PHD, and CH3CH2PD2 have been recorded in the range 18.0 to 40.0 GHz. A-type transitions were observed and assigned for both gauche and trans conformers of ethylphosphine, and b-type transitions observed and assigned for the gauche conformer. The dipole moment components for the gauche conformer were determined from the Stark effect to be: vertical-barμ/suba/vertical-bar= 0.86+-0.01, vertical-barμ/subb/vertical-bar=0.73+-0.07, vertical-barμ/subc/vertical-bar=0.45+-0.05, and vertical-barμ/subt/vertical-bar=1.22+-0.07 D. For the trans conformers, there was only one component of the dipole moment and it had a value of vertical-barμ/suba/vertical-bar= vertical-barμ/subt/vertical-bar=1.226+-0.005 D. The relative intensity of nine pairs of lines for the gauche and trans were measured at room temperature, and from the ratio of intensities it was found that ethylphosphine exists as a 45% gauche and 55% trans mixture with an energy difference of 200+-100 cm-1 and the trans the more stable conformer. With reasonable assumptions for the ethyl moiety, the following structural parameters were calculated: angleCCP=110.1+-0.2degree, r/sub PC/=1.880+-0.0002 A and PH2 dihedral angle = 61+-2degree and for the gauche conformer angleCCP= 115.2+-0.2degree, r/sub PC/=1.876+-0.002 A and PH2 dihedral angle = 180+-2degree