Rotational spectrum of the trimethylphosphine–hydrogen fluoride complex

The rotational spectra of the four isotopomers (CH3)3P⋯HF, (CH3)3P⋯DF, (CH3)2(13CH3)P⋯HF and (CD3)3P⋯HF of a hydrogen-bonded complex formed by trimethylphosphine and hydrogen fluoride have been observed by pulsed-nozzle Fourier-transform microwave spectroscopy. The H, F nuclear spin–spin coupling constant DHFaa and the D-nuclear quadrupole coupling constant χDaa were determined for the first two isotopomers. Interpretation of these coupling constants in conjunction with rotational constants and centrifugal distortion constants allows the conclusion that the intermolecular binding is relatively weak (kσ=17.2(3) N m−1), with only a small lengthening δr≈0.012 Å of the HF bond on formation of a symmetric-top complex (CH3)3P⋯HF having r(P⋯F)=3.120(2) Å.