Knowledge Bank

The vibrational spectra of the compound N,P,P,P-tetramethylphosphine imide and its N-methyl-$d3$ analogue have been found to be consistent only with a $Cs$ structure whose vibrational potential function exhibits large deviations from local $C3v$ symmetry at both phosphorus and nitrogen. All 48 vibrational fundamentals expected under $Cs$ molecular point symmetry have been assigned based on group frequencies, isotopic frequency shifts, and Raman depolarization measurements. The P:N torsional modes have been assigned at 112 and $100cm-1$ in the light and heavy molecules, respectively, and threefold barriers of 2.06 and 2.42 kcals/mole, respectively, have been calculated from these assignments.