Sulfur LII,III emission spectra and molecular orbital studies of sulfur compounds

Abstract

The fluorescent sulfur L_II,III emission spectra have been quantitatively measured and analyzed for the relative strengths (radiative yields) of the allowed transitions, and for the corresponding emission linewidths. These were investigated for the sulfur compounds in the solid, vapor, and gas states—Na₂SO₄, K₂SO₄, CdSO₄, Na₂SO₃, K₂SO₃, C₄H₄S, H₂S, SO₂, and SF₆. The S L_II,III spectra for the solid compounds (all strongly ionic) revealed essentially the same localized molecular orbital character about a central sulfur atom as for the molecular compounds—showing no significant influence of the cations and no evidence of crystal band structure. The measured molecular orbital energies and radiative yields were found to be generally consistent with the eigenvalue and eigenvector calculations based upon current CNDO and ab initio molecular orbital approximation methods. The measured sulfur L_II,III spectra for the compounds reported in this paper have been interpreted according to the valence orbital configuration as obtained from the CNDO/2 method. This is done while recognizing that other reported molecular orbital calculations on these molecules often indicate different orderings. The molecular orbital energies as derived from the L_II,III spectra have also been compared with those obtained from photoelectron spectroscopy, demonstrating, generally, very good agreement between these two methods. Because the L_II,III spectra for second row elements probe the 3s and the 3d character of the valence band and the K_β spectra probe the 3p character of the valence band, it has been found very useful to combine the results of these x‐ray emission techniques in order to gain a complete analysis of valence band electronic populations and symmetries. It has been shown that the L_II,III emission analysis can be a uniquely powerful tool for the determination of the role of the 3d atomic orbital in the chemical bonding of the second‐row elements.