The Jahn Teller and pseudo-Jahn Teller effect in the dark \~{A} state of the nitrate radical NO$_{3}$

Despite its apparent simple molecular structure, the lowest electronic states of the nitrate radical NO$_{3}$ remain poorly understood. In particular, the three lowest states of the radical provide a benchmark for testing models of the Jahn-Teller (JT) and pseudo-JT effects. The dark \~{A} state of NO$_{3}$ undergoes strong JT distortion, suggesting that models with only linear and quadratic vibronic couplings are inadequate. We present cavity ringdown (CRD) and integrated cavity output (ICOS) spectra of the forbidden $\mathop A\limits^\sim { }^2E"\leftarrow \mathop X\limits^\sim { }^2A_2 '$ transition (preliminary report in Deev, et. al. \textit{J.Chem. Phys}., 2005. 122:224305) and compare them to a simulation based on a model Hamiltonian developed by Koppel, Domcke and Cederbaum that incorporates both JT and PJT couplings. New insights into the pseudo-JT effect among the lowest states are gained by examination of intensity-borrowing mechanisms for the observed vibronic bands.