Rotational spectrum of phosphonium iodide vapour

Abstract

The ground-state rotational spectrum of the associated species (PH₃, HI) has been observed in the vapour above solid phosphonium iodide by means of pulsed-nozzle, Fourier-transform microwave spectroscopy. To fit the observed hyperfine frequencies of this symmetric-top isotopomer it is necessary to allow for the variation of the iodine nuclear quadrupole coupling constant with J and K as well as to take into account iodine spin–rotation coupling. Interpretation of the spectroscopic constants of the three isotopomers (PH₃, Hl), (PH₃, Dl) and (PH₂D, Hl) leads to the conclusion that the observed species have nuclei in the order H₃P ⋯ Hl and, for the first of the three, that r(P ⋯ l)= 4.3822 Å. For the series HX the order of the electrophilicity is F > Cl > CN > Br > l while the order of the nucleophilicity is HCN > HF > HCl ≈ Hl.