Electron Diffraction Study of Monomethyl- and Dimethylphosphine

The structural parameters of gaseous monomethyl- and dimethylphosphine were determined by the sector-microphotometer method of electron diffraction. Center of gravity bond distances and standard errors for the two molecules were, respectively: rCP=1.858±0.003 A and 1.853±0.003 A; rCH=1.094±0.008 A and 1.097±0.007 A; rPH=1.423±0.007 A and 1.445±0.02 A. The angles P–C–H were 109.6±1° and 109.8±0.7°. In dimethylphosphine the angle C–P–C was 99.2±0.6°. The methyl groups were found to be in staggered conformations. The distances and root-mean-square amplitudes of vibration agreed well with the values determined in recent studies of phosphine and trimethylphosphine.