Photoelectron spectra of halides. Part II. High-resolution spectra of the boron trihalides

Abstract

The photoelectron spectra of boron trifluoride, trichloride, tribromide, and tri-iodide have been obtained by use of a cylindrical deflection analyser instrument and He^I resonance radiation. Vertical ionization potentials, and in most cases adiabatic ionization potential also, are tabulated. Vibrational fine structure is observed in the BF₃ and BCl₃ spectra, and some of the bands of BBr₃ and Bl₃ show splittings ascribed to spin–orbit coupling. The spectra are interpreted on the basis of band splittings, fine structure, and correlation with the results of calculations; the BF₃ assignment is in good agreement with recent Gaussian basis molecular orbital calculations. From the energies of the π orbitals it is deduced that the molecular π stablisation energy follows the sequence BF₃ > BCl₃ > (BBr₃∼ Bl₃), but evidence is presented that this is still consistent with the opposite sequence of π-electron delocalisation.