Cavity-ring-down spectroscopy of the heavy ozone isotopologue 18O3: Analysis of a high energy band near 95% of the dissociation threshold

Highlights: • Cavity ring down spectroscopy of ¹⁸O₃ between 7920 and 7985 cm⁻¹. • 259 transitions assigned to 7ν₁+ν₃ vibrational band. • Upper vibrational state located a few% below the dissociation limit at 8620 cm⁻¹. • Effective operator modeling of the spectra. • Good agreement with ab initio values for the band center and rotational constants. The absorption spectrum of the ¹⁸O₃ isotopologue of ozone was recorded by cavity-ring-down spectroscopy between 7920 and 7985 cm⁻¹ with a routine noise equivalent absorption, α_min, on the order of a few 10⁻¹¹ cm⁻¹. This permitted to detect and analyze an extremely weak vibrational band assigned as 7ν₁+ν₃ following predictions from the ab initio potential energy surface reported in J Chem Phys 2013;139:134307. This is the most excited rovibrational band of the ¹⁸O₃ isotopologue detected so far. In total, 259 ro-vibrational transitions were measured and modeled using an effective Hamiltonian model. The vibrational dipole transition moment parameter of the band deduced from the analysis and the fit to 177 experimental line intensities was evaluated as 2.6 × 10⁻⁶ Debye. The absorption coefficient of the recorded pure ¹⁸O₃ spectrum was found significantly smaller compared to that of the ¹⁶O₃ in the same range. The set of 171 upper state energies experimentally determined cover the range from 92.6% (at J = 1) to 97% (at J = 26) of the first dissociation threshold D₀. The comparison with ab initio predictions for the band origin and ʋ-dependent rotational constants is discussed. An absorption line list containing 477 transitions is provided as Supplementary material for the 7ν₁+ν₃ band.