The high sensitivity absorption spectrum of ozone (18O3 and 16O3) near 7800 cm−1: Identification of the 3A2(0 0 0)–X(1 1 0) hot band superimposed to very weak vibrational bands

The very weak absorption spectra of 18O3 and 16O3 have been recorded between 7700 and 7920 cm−1 by high sensitivity cavity ring down spectroscopy (αmin ∼10−10 cm−1). The upper limit of the investigated region is only 6% below the dissociation energy. The spectrum consists in the superposition of very weak vibrational bands and unexpected broad absorption features which dominate in the case of the 18O3 isotopologue. From recordings at temperatures ranging from 294 to 354 K, the broad features were identified as due to the 3A2(0 0 0)–X1A1(1 1 0) hot band. The rovibronic levels of the 3A2(0 0 0) state are predissociated and the widths of the corresponding lines range from 0.02 to at least 0.5 cm−1.