The high sensitivity absorption spectrum of ozone ( 18O 3 and 16O 3) near 7800 cm −1: Identification of the 3A 2(0 0 0)–X(1 1 0) hot band superimposed to very weak vibrational bands

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The very weak absorption spectra of 18O 3 and 16O 3 have been recorded between 7700 and 7920 cm −1 by high sensitivity cavity ring down spectroscopy ( α min ∼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 18O 3 isotopologue. From recordings at temperatures ranging from 294 to 354 K, the broad features were identified as due to the 3A 2(0 0 0)–X 1A 1(1 1 0) hot band. The rovibronic levels of the 3A 2(0 0 0) state are predissociated and the widths of the corresponding lines range from 0.02 to at least 0.5 cm −1.