Cavity ringdown spectrum of the forbidden A~2E' -X~2A'_2 transition of NO_3:Evidence for static Jahn-Teller distortion in the A state

摘要

The Jahn-Teller effect in the first two excited states of the nitrate radical NO_3 has yet to be experimentally elucidated.In this paper,direct evidence of strong Jahn-Teller interactions in the A state is presented from the first complete absorption spectrum of the A~2E"<- X~2A'_2 transition of NO_3 in the gas phase in the region 5900-9000 cm~(-1),at moderate resolution (0.15 cm~(-1)).The observed spectrum is consistent with Herzberg-Teller selection rules,and reveals strong linear and quadratic Jahn-Teller interactions in the A state.Several of the vibronic bands have been tentatively assigned,including nu_2,nu_3,an irregular progression in nu_4,and combination bands involving nu_l.Our assignments are consistent with the previous works of Weaver et al.[A.Weaver,D.W.Arnold,S.E.Bradforth,and D.M.Neumark,J.Chem.Phys.94,1740 (1991)] and Hirota et al.[E.Hirota,T.Ishiwata,K.Kawaguchi,M.Fujitake,N.Ohashi,and I.Tanaka,J.Phys.Chem.107,2829 (1997)] The band origin is not observed,in accord with the selection rules,but is determined to be T_0=7064 cm~(-1) from the observation of the 4_1~0 hot band at 6695.7 cm~(-1).Rotational contour analysis of this band indicates that the upper state is an asymmetric rotor,establishing that NO_3 undergoes static Jahn-Teller distortion in the ground vibrational level of the A state.