Spectroscopic studies of the Jahn-Teller effect in the Ã2E″ state of the nitrate radical NO3

We report spectra of the forbidden origin and several hot bands of the A ˜ 2 E ″ ← X ˜ 2 A 2 ′ transition of NO3 using cavity ringdown and enhanced absorption spectroscopies. We directly observed the origin at T0(Ã) = 7062.25(50) cm−1, which arises from a magnetic-dipole or rotationally-forbidden transition. We used this assignment to estimate fundamental frequencies in the à state. The Jahn Teller (JT) effect splits the vibronic levels E(Γev) of the ν 4 ′ = 1, E″⊗e′ manifold. We measured E(E″)–E( A 1 ″ ) to be 1.6(1.9) cm−1 implying weak JT effect in the Q4 mode. We discuss the possible assignment of a band observed near the origin to either spin-orbit splitting or an A 2 ″ level.