First high resolution analysis of the 2v(1), 2v(3), and v(1) + v(3) bands of (SO2)-O-18

We report the results of a highly accurate, (1–3)×10⁻⁴ cm⁻¹, ro-vibrational analysis of the S¹⁸O₂ molecule in the spectral region of 2100–2700 cm⁻¹. More than 2910, 2130, and 1390 transitions belonging to the 2ν₁, ν₁+ν₃, and 2ν₃ bands were assigned for the first time with the values of quantum numbers J^max./K_a ^max. equal to 67/26, 81/25 and 53/16, respectively. The weighted fit of experimentally assigned transitions was made with the Hamiltonian model which takes into account Coriolis resonance interactions between the vibrational states (v₁v₂v₃) and (v₁∓1v₂v₃±1) and Fermi interactions between the states (v₁v₂v₃) and (v₁∓1v₂±2v₃). To make the ro-vibrational analysis physically more suitable, the initial values of main spectroscopic parameters have been estimated theoretically. Finally, the set of 43 spectroscopic parameters obtained from the fit reproduces values of 2384 initial “experimental” ro-vibrational energy levels (more than 6430 transitions assigned in the experimental spectra) with the rms=1.74×10⁻⁴cm⁻¹.