He I photoelectron spectroscopy study on the electronic structure of bromine nitrate, BrONO2

The gas phase He I photoelectron (PE) spectrum of BrONO2, an important atmospheric trace species, is reported for the first time. The assignment for the PE spectral bands of BrONO2 is made on the basis of band shape, fine vibrational structures, and ab initio calculation using the Gaussian 86 321G basis set level. From the expanded PE spectra between 10.50 and 12.00 eV and between 12.00 and 14.50 eV, it is seen that the spin-orbital splitting reflected on the HOMO 8a'' (33) orbital is 0.31 eV and comes from ionization of lone pair electrons of bromine atoms in the molecule. The vibrational spacings 1050 +/- 60 cm(-1) and 1130 +/- 60 cm(-1) on the band centered near 12.50 eV are ascribed to ionization of electrons of both 22a' and 21a' orbitals which have the dominant contribution of an -NO2 atomic group in the molecule. The band centered near 13.12 eV with vibrational spacing 670 +/- 60 cm(-1) is designated to-ionization of electrons of 6a'' (28) orbital which has a dominant contribution of a -BrO atomic group and belongs to a weak Pi bond in the molecule.