The valence shell electronic states of trimethylene sulphide studied by photoabsorption and ab initio multireference configuration interaction calculations

The absolute photoabsorption cross section of trimethylene sulphide has been measured between threshold and 30 eV using monochromated synchrotron radiation. Below the ionization threshold the spectrum exhibits numerous sharp peaks associated with Rydberg states belonging to series converging onto the (X) over tilde (2)B(1) limit. At excitation energies above the ionization threshold at 8.655 eV intravalence transitions play a dominant role, resulting in the appearance of prominent broad bands. Ab initio multireference configuration interaction calculations have been performed to obtain excitation energies for valence electron transitions into Rydberg or virtual valence orbitals. These theoretical predictions have enabled assignments to be proposed for most of the structure due to Rydberg series converging onto the (X) over tilde (2)B(1) limit. The calculations show that configuration interaction is important in the description of many of the excited states. This is particularly evident close to threshold where the theoretical results suggest that the observed, highly irregular, structure may be attributed to two Rydberg transitions and an intravalence transition. The calculations also establish that both of the dipole allowed 4b(1) -> nda(1) B(1) Rydberg series should contribute to the absorption spectrum.