K edge absorption spectra of sulphur in vapour, molecular and polymerized solid phases

X-ray K absorption spectra of sulphur have been studied in its vapour, molecular and polymerized solid phases. The vapour phase of sulphur containing S-2 molecules yields a K spectrum which is similar to that of the O-2 molecule. This observation suggests a (3) Sigma(g)(-) ground state of S-2, which is in agreement with that obtained from optical spectra. Different line splittings in the spectra of these molecules are discussed in the light of the p orbital and s-p orbital energy differences of some second- and third-period elements. While the condensed phase spectrum of O-2 remains unchanged, the observed K spectrum of condensed S-2 differs considerably from its vapour phase. This abrupt change in the bonding between the S atoms in the condensed phase is typical behaviour of sulphur and indicates the formation of two directional covalent bonds and creation of 3s(2) and 3p(2) lone pairs. This behaviour is, in fact, a clear distinction between the chemistries of sulphur and that of its homologue oxygen. The cyclic and chain forms of sulphur show some similarity in sigma* line structure and a marked difference in their near-edge structure due to a different number of S atoms surrounding a central atom in these allotropic forms.