Inter- and intramolecular electronic transfer on formation of H3P···ICl as determined by rotational spectroscopy

Abstract

Ground-state rotational spectra of the three isotopomers H3P···I35Cl, H3P···I 37Cl and D3P···I35Cl of a symmetric-top complex formed between phosphine and iodine monochloride were observed by pulsed-nozzle, Fourier transform microwave spectroscopy. The spectroscopic constants B0, DJ, DJK, χaa(I), χaa(Cl), Maa(I) and Mbb(I) were determined in each case. Changes in B0 on isotopic substitution established that the nuclei lie in the order H3P···ICl, with the distance r(P···I)=2.963(1) Å. The changes in the halogen nuclear quadrupole coupling constants χaa(I) and χaa(Cl) from their counterparts in the free ICl molecule led to the conclusion that a fraction δi =0.144(7) of an electron is transferred from P to I on complex formation and that the polarization of ICl by PH3 is equivalent to the intramolecular transfer of a fraction δp(Cl)=0.157(2) from I to Cl. The complex is about as strongly bound as H3N···HCl, when the intermolecular stretching force constant kσ is used as a criterion. It is found that the distance r(P···I) contracts by 0.017 Å between H3P···I35Cl and D3P···I35Cl. The systematic variation of δi within a series of complexes B···ICl is discussed.