Photoionization and dissociative ionization of the nitrate radical studied by threshold photoelectron photoion coincidence spectroscopy

Abstract

The nitrate radical has been a benchmark system for quant. testing ab initio treatments of the Jahn-Teller Effect and nonadiabatic interactions. The spectroscopy of its cation NO_3+ may provide an even more challenging system. Ab initio calcns. predict that there are four low lying electronic states, three of E symmetry exhibiting the Jahn-Teller Effect that lie 1-2 eV above the ground state. There have been two earlier low resoln. expts. using photoionization mass spectrometry and photoelectron spectroscopy. These expts. are consistent with adiabatic calcns. indicating that the ground state is a sym. D3h geometry with an IP= 12.55 eV; however, they give conflicting results on the existence of the excited states. We have performed VUV Threshold PhotoElectron-PhotoIon Coincidence (T-PEPICO) spectroscopy expts. on the radical cation NO_3+ using the DESIRS beamline at Synchrotron SOLEIL. The DELICIOUS 3 spectrometer provides photoelectron and photoion imaging coincidence detection. We have obsd. a high resoln. threshold photoelectron spectrum of the stable ground state of NO_3+. At slightly higher energies, we find a strong absorption with partially resolved vibronic bands leading exclusively to dissociative ionization. We characterize the spectroscopy of the excited states of NO_3+ and the dissocn. dynamics leading to the formation of NO_2+ + O products and report preliminary calcns.