The electronically excited and ionic states of sulphur dioxide: an ab initio molecular orbital CI study and comparison with spectral data

Abstract

The electronically excited singlet and triplet valence, and Rydberg states, in the excitation energy range 1–16 eV, have been determined for sulphur dioxide, by large scale CI methods. Theoretical values for the excitation energies and oscillator strengths for a range of Rydberg states converging on the first six IPs have been calculated. The sequence of ionic states have been re-determined by CI and TDA calculations; the results support the recent study by Li et al. [J. Chem. Phys., 120, 4677 (2004)], that the sequence of IPs should be reordered to

. Several adiabatic excited and ionized state equilibrium structures were determined using CCSD(T) and CI methods. Several bases were used, including one containing the s,p,d-components of a cc-pV5Z basis set; however, an alternative quadruple zeta basis set augmented by diffuse and Rydberg functions provided better coverage of the lower excited states, owing to a wider s,p,d-range of virtual orbitals.

The gap in the published experimental VUV spectrum between 992 and 1078 Å has been completed using both new data, and re-evaluation of the Price and Simpson [Proc. Roy. Soc. Ser. A, 165, 272 (1938)] photographic data. A number of new Rydberg states in both the gap and nearby regions have been identified. The experimental assignment of the electronic spectrum is critically assessed in some detail. Assignment of the lower singlet and triplet manifolds and comparison of the theoretical intensity envelope with the VUV absorption and photoionization spectra has been made.

Acknowledgements

We are grateful to the Edinburgh Parallel Computing Centre for access to the Sunfire 6800 UltraSPARC-III parallel processor (ness.epcc.ed.ac.uk), and to Dr D.M.P. Holland (Daresbury Laboratory) for access to raw spectral data, and helpful discussion; Professor J. Orphal (Université Paris-Sud, Orsay), and Professor J.B. Nee (National Central University, Chung-Li, Taiwan) for unpublished photoionization and absorption data, and helpful discussion; Dr P.J. Camp and Dr S. Hinchley (Edinburgh) for assistance with some of the figures.