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

The spectroscopy and predissociation of the 3A2(0 0 0) state of 18O3 are investigated from the analysis of the absorption spectrum of the 3A2(0 0 0)←X˜1A1(110) 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 3A2(0 0 0) upper state. Most of the transitions exhibit a clear broadening due to the predissociation of the 3A2(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 3A2(0 0 0) level and high lying dissociative vibrational levels of the X˜1A1 electronic ground state, with (i) the J and Ka rotational quantum numbers and (ii) the energy gap between the coupled pair of rotational levels. From the predicted energies of the X˜1A1 vibrational states and their vibrational overlap with the 3A2(0 0 0) state, a few of these X˜1A1 vibrational levels are identified as possibly responsible for the 3A2(0 0 0) predissociation. The predissociative mechanism in 18O3 is compared to that taking place in 16O3.

► We recorded the 18O3 absorption spectrum between 7600 and 7920 cm−1 by cw-CRDS. ► We observed broad absorption lines assigned to the 3A2(0 0 0)←X˜1A1(110) hot band. ► Predissociation rates are obtained from the fit of selected transitions. ► Predissociation is linked to the coupling of 3A2(0 0 0) with doorway states of X˜1A1. ► Few doorway states are identified as possible candidates for the coupling.