Variationally Computed Line Lists for SO2 and SO3

The work presented in this thesis concerns the production of high-temperature spectroscopic line lists for the SO2 and SO3 molecules, for the purposes of astrophysical, terrestrial and industrial applications. Both line lists are computed using ab initio computational methods to calculate rovibrational energy levels and dipole moment transition intensities. The hot SO2 line list is computed using the DVR3D program suite, optimised to work efficiently with the molecule, and by making use of high performance computing. The calculations are based on an empirically refined ab initio potential energy surface (PES), and a purely ab initio dipole moment surface (DMS). Results are compared to previous ab initio studies and available experimental data. The final line list can be used in spectroscopic models for temperatures up to and including 1500 K. A preliminary, room-temperature line list for SO3 is calculated using the TROVE program, in conjunction with a purely ab initio PES and DMS. The results are compared to available experimentally derived energy level data. These are then used to empirically refine the ab initio PES, which is subsequently employed in the calculation of the complete, hot line list, suitable for modelling SO3 spectra up to 773.15 K. Preliminary comparisons are made with experimental high-temperature measurements, and the quality of the ab initio DMS is discussed. In addition, the rotational behaviour of the SO3 molecule is investigated from a theoretical perspective using the synthetic SO3 line list, where the ‘forbidden’ rotational spectrum is analysed. The formation of so-called 6-fold rotational energy clusters at high rotational excitation is also predicted, the dynamics of which are analysed both quantum mechanically and semi-classically. The potential applications and limitations of both line lists is outlined, and implications for further work are also discussed.