Spectroscopy and dynamics of the nitrate cation NO₃+

Abstract

The nitrate radical NO₃ has been an important benchmark system for theor. treatments of the impact of nonadiabatic effects on large amplitude vibrational motion. The nitrate radical has D_(3h) symmetry with a nondegenerate ground state and two degenerate excited states that are Jahn-Teller active, with significant non-adiabatic coupling among all three of the lowest states. Neutral NO₃ remains a perplexing mol., but even less is known about its cation, NO₃+. Like the neutral radical, the cation has a ground state (IP = 12.55 eV) that is nondegenerate state with D_(3h) symmetry; however, it has three low-lying electronically-excited states that are all predicted to be Jahn-Teller active. The low frequency vibrations on these surfaces are thus perturbed by strong non-adiabatic effects; furthermore, they may couple to dissociative states and undergo predissocn. We describe Threshold PhotoElectron PhotoIonization Coincidence (t- PEPICO) Spectroscopy expts. performed on the DELICIOUS3 coincidence spectrometer on the DESIRS beamline at the Soleil Synchrotron. Coincidence methods using velocity-map imaging of the photoelectrons and Wiley-McLaren time-offlight mass spectrometry allow us to begin to unravel the spectroscopic and dynamical processes occurring upon photoionization into the excited state manifold. We have also performed high level calcns. using Equation of Motion methods to assign the obsd. spectra and explain the obsd. dynamics.