Photoelectron spectroscopic studies of some nitrosyl and nitryl halides and nitric acid

The He(I) photoelectron spectra of the compounds FNO, ClNO, BrNO, FNO₂ and ClNO₂ have been recorded on an instrument specifically designed to study reactive and short-lived species. The spectrum of HNO₃ (isoelectronic with the nitryl halides) is included for comparison. The spectra of the nitrosyl halides are interpreted by reference to SCF-MO calculations, by correlation with the known levels of NO, and by consideration of the electronic effect of the halide (X) substituent. The resulting assignments are in accord with weak bonding between the X and NO moieties. The assignments for the nitryl halides and nitric acid are assisted by correlation with the known levels of NO₂, by consideration of the electronic effects of the X substituent, by an analysis of vibrational structure, and by CNDO type MO calculations. On the basis of our assignments for these latter molecules we propose a reassignment of the photoelectron spectrum of CH₃NO₂.