Theoretical investigation of the absorption and ionization spectrum of the super greenhouse gas SF5CF3.

SF5CF3, recently found in the Earth's atmosphere, is an extremely potent greenhouse gas. Its behaviour under irradiation, as in the upper atmosphere, is of great importance for the possible impact on the global climate. The vertical absorption spectrum of the title compound is studied by various single- and multi-reference ab initio methods and the results are compared to experiments. The best results for valence states are obtained by the multi-state complete active space second order perturbation theory (MS-CASPT2) approach. In contrast, the popular time-dependent density functional theory (TDDFT) gives very poor results. Multi-reference configuration interaction (MRCI) does not yield very accurate energies because only a limited number of valence electrons can be included in the correlation treatment. The Rydberg states are calculated very accurately and efficiently by a frozen-core multi-configuration self-consistent field (FC-MCSCF) method. The accuracy is assessed by quantum defect theory and the experimental and ab initio calculated first ionization potential. The photoelectron spectrum is investigated by the outer-valence Green's functions (OVGF) method. The simulated spectrum is in excellent agreement with a recent experiment.