High-temperature photoelectron spectroscopy. A study of SiS(X 1Σ+)

Abstract

The He I photoelectron spectrum of SiS(X ¹Σ⁺) has been recorded and interpreted with the aid of ab initio configuration interaction calculations. Five bands associated with this molecule were observed below 21 eV ionization energy, whereas only three are expected on the basis of Koopmans' theorem. Consequently, SiS represents an example of the breakdown of the one-electron ionization model, and the presence of five bands in the experimental spectrum is rationalised in terms of an ionic-state configuration interaction mechanism. Vibrational structure has been resolved in the first and third photoelectron bands and analysis of this structure leads to values of r_e, _e and D_e in the X ²Π and B ²Σ⁺ states of SiS⁺.