Predissociation and spectroscopy of the 3A2(0 0 0) state of 18O3 from CRDS spectra of the 3A2(0 0 0)←X1A1(1 1 0) hot band near 7900 cm−1☆

Abstract The spectroscopy and predissociation of the 3 A 2 (0 0 0) state of 18 O 3 are investigated from the analysis of the absorption spectrum of the 3 A 2 (0 0 0)← X ˜ 1 A 1 ( 1 1 0 ) hot band recorded by high sensitivity cw-CRDS between 7600 and 7920 cm −1 . The noise equivalent absorption of the recordings is on the order of 1×10 −10  cm −1 . Forty transitions could be rotationally assigned and their line positions were used to derive approximate spectroscopic parameters of the 3 A 2 (0 0 0) upper state. Most of the transitions exhibit a clear broadening due to the predissociation of the 3 A 2 (0 0 0) upper state at 9573.61 cm −1 . The width of the Lorentzian component (from 0.02 up to more than 0.5 cm −1 ) was retrieved for some of the assigned transitions. The variation of the corresponding predissociation rates is due to the dependence of the spin–orbit coupling between the 3 A 2 (0 0 0) level and high lying dissociative vibrational levels of the X ˜ 1 A 1 electronic ground state, with (i) the J and K a rotational quantum numbers and (ii) the energy gap between the coupled pair of rotational levels. From the predicted energies of the X ˜ 1 A 1 vibrational states and their vibrational overlap with the 3 A 2 (0 0 0) state, a few of these X ˜ 1 A 1 vibrational levels are identified as possibly responsible for the 3 A 2 (0 0 0) predissociation. The predissociative mechanism in 18 O 3 is compared to that taking place in 16 O 3 .