FTS high resolution spectra of 16O3 in 3500 and 5500 cm−1 regions. First example of new theoretical modelling for a polyad of strongly coupled states

The infrared spectrum of 16O3 has been revisited in the ranges 3300-3600 cm−1 and 5200-5600 cm−1, recorded by the Fourier Transform Spectrometer of Reims, with an improved signal/noise ratio. In the lower spectral range the weak 2ν1+2ν2 band is observed and assigned for the first time. This allowed for completing the triad of strongly interacting (220), (121), and (022) states. The resonance interaction parameters for this triad were derived from the molecular potential energy surface using high-order Contact Transformation method. This involves Darling-Dennison resonances between (220) and (022) vibration A-states, and Coriolis resonances between (121) B-state and A-states. Altogether 18 coupling parameters were fixed to these theoretically predicted values that allowed avoiding problems of ambiguities while fitting strongly correlated parameters. The remaining small perturbations of a few Ka=5 transitions of the ν1+2ν2+ν3 band were explained by accidental Coriolis resonance of (121) with the (050) dark state. This mixed half theoretical/half empirical model (with 39 fitted and 77 theoretically constrained parameters) developed in this work for the first time allows an excellent description of 1897 line positions with the rms deviation ∼0.001 cm−1 closed to the experimental precision. The intensities of two new hot bands ν2+4ν3−ν3 and ν1+ν2+3ν3−ν1 that fall in this range were also observed and modelled, thanks to a better signal to noise ratio.In addition, the 5200-5600 cm−1 region has also been revisited, showing for the first time the (321) state which was considered as “dark” one in the previous analysis. Effective Hamiltonian parameters were derived for strongly coupled (213)/(114)/(321) upper states including (080) as a dark one.The transition moment parameters of all newly observed and assigned bands were derived resulting to average rms deviation for intensities of ∼8% and 13% for the cold and the hot bands, respectively, in the lower range and of ∼15% for the bands in the upper range that is close to experimental accuracy for weak transitions.

► FTS high resolution spectra of 16O3 in the 3500 and 5500 cm−1 ranges are revisited. ► Theoretical modelling for a polyad of strongly coupled states with resonance parameters predicted from potential function. ► Hamiltonian and Transition moment parameters for (220),(121),(022),(050) are given. ► New hot bands with {(001),(100)} as lower levels are assigned.