THE JAHN-TELLER EFFECT IN NO$_3$: SHEDDING NEW LIGHT ON THE DARK $\widetilde{A} ^2 E^{\prime \prime}$ STATE

Author Institution: Arthur Amos Noyes Laboratory of Chemical Physics, California Institute of Technology, Pasadena CA 91125; Department of Chemistry, University of Texas, Austin, TX, 78712The Jahn-Teller Effect in the lowest excited states of the nitrate radical NO$_3$ remains poorly understood. In this paper, we examine the first excited state, $\widetilde{A} ^2 E^{\prime \prime}$, in a joint experimental and theoretical study. The forbidden $\widetilde{A} ^2 E^{\prime \prime} \leftarrow \widetilde{X} ^2 A_2^{\prime}$ transition is recorded by Near Infrared Cavity Ringdown Spectroscopy (CRDS) at medium resolution from 6000 to $>$10,000 cm$^{-1}$, extending and refining our preliminary results. We observe over 30 major vibronic bands, most with resolvable rotational structure. Tentative assignments are made on the basis of high level EOMIP-CCSD(T) calculations of the vibronic Hamiltonian, which includes up to quartic terms. Our results indicate that the $\widetilde{A}$ state undergoes static Jahn-Teller distortion, with strong vibronic coupling among both degenerate modes and the symmetric stretch. The Jahn-Teller effect in NO$_3$ appears to be complex and unusual, and remains a difficult but fascinating challenge