First far-infrared high-resolution analysis of the ν<SUB>2</SUB> band of sulphur dioxide <SUP>32</SUP>S<SUP>16</SUP>O<SUP>18</SUP>O and <SUP>32</SUP>S<SUP>18</SUP>O<SUB>2</SUB>

International audienceHigh-resolution Fourier transform spectra of 18O-enriched isotopic samples of sulphur dioxide (32S16O18O and 32S18O2) have been recorded at 0.00102 cm-1 resolution in the 400-620 cm-1 region at Synchrotron SOLEIL. These spectra have been recorded at low temperature 185 K using a 3.14 m optical path length cryogenic cell. This enables the first detailed infrared analysis of the ν2 bands of the 32S16O18O and 32S18O2 isotopologues of sulphur dioxide located at 507.36541(1) and 496.59988(1) cm-1, respectively. Using a Watson-type Hamiltonian model to compute the upper and lower state energy levels, it was possible to reproduce the observed transitions. For both species, accurate rotational and centrifugal distortion constants were derived for the upper (0,1,0) vibrational state, while those of the (0,0,0) ground state were significantly updated. For this task, we combined the results of the present infrared measurements with the available literature microwave data in the (0,0,0) and (0,1,0) vibrational states. Finally, we took the opportunity of this study to compare the quality of the fit using an A- and S-type reduction for the Watson Hamiltonian