A STUDY OF HEI PHOTOELECTRON-SPECTROSCOPY ON THE ELECTRONIC-STRUCTUREOF THE NITRATE FREE-RADICAL NO3

A continuous nitrate free radical (NO3) beam is produced in situ by th e pyrolysis of pure gas phase N2O5 at 280 degrees C (+/-0.5 degrees C) in a double-heater inlet system on a double-chamber UPS Machine-II wh ich was built specifically to detect transient species. The HeI photoe lectron spectroscopy (PES) of the NO3 radical is recorded for the firs t time. Five obvious bands emerge on the PE spectrum of the NO3 radica l. A very sharp peak with the lowest ionization energy at 12.55+/-0.01 eV originates from electron ionization of the HOMO for the NO3 radica l, corresponding to the NO3+((1)A(1)')<--NO3 ((2)A(2)') transition. To assign the bands of the PE spectrum of the NO3 radical, the improved density functional theory (DFT) calculation based on the Amsterdam den sity functional (ADF) program package has been carried out according t o D-3h symmetry for the neutral ground state of the NO3 radical and th e equilibrium geometries of several ionic states of the cationic speci es. The ionization energies computed are in reasonable agreement with the PES experimental ionization energies. Both PES experimental and DF T calculation provide evidence on the lowest triplet and singlet state s of the NO3+ cation. (C) 1997 American Institute of Physics.