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

The absolute photoabsorption cross section of ethylene sulphide has been measured between threshold and 30 eV using monochromated synchrotron radiation. Below the ionisation threshold the spectrum exhibits numerous sharp peaks associated with Rydberg states belonging to series converging onto the X∼2B1 limit. At excitation energies above the ionisation threshold at 9 eV intravalence transitions play a dominant role, resulting in the appearance of prominent broad bands. Much weaker structure ascribed to Rydberg states associated with excitation from the 4b2, 8a1 or 2b1 orbitals is also discernible. 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∼2B1 limit. The calculations show that configuration interaction is important in the description of many of the excited states.