Phosphorus microwave spectrum

The microwave spectrum of aminodifluorophosphine (141) indicates a planar PNHg group with a HNH bond angle of 117.2° and total jtx 2.58 The spectra of four phosphorus trihalides are also reported. ... 

Odom, J.D., Kalasinsky, V.F and Durig, J.R. (1975) Spectra and stmcture of phosphorus-boron compounds. XI. Microwave spectrum, stmcture, dipole moment, and barrier to internal rotation in phosphine-trifluoroborane./fwrg. Chem., 14, 2837-2839. 

The radiofrequency spectrum of phosphine has been measured in a molecular beam electric resonance spectrometer. The suspected inversion doubling was not observed its dipole moment (ju.) was 0.574 D. The calculated rotational barrier between the staggered and eclipsed conformers of methylphosphine is 1.83 and 1.71 kcal mol, in agreement with the experimental value of 1.96 from microwave measurements. An orbital-by-orbital analysis of the changes which occur upon rotation suggests a hydrogen-bond contribution when the phosphorus lone pair of electrons and a CH bond are appropriately orientated.The existence of a 1—2° tilt of a methyl group towards the phosphorus lone pair of electrons in methylphosphines (138) was a conclusion drawn from a microwave study... 

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