1. See f. i. Senning, A. (ed.): Sulfur in organic and inorganic chemistry, Vol. 1. New York: Marcel Dekker 1971; Price, C. C., Oae, S.: Sulfur bonding. New York: Ronald Press 1962
2. Turner, D. W., Baker, A. D., Baker, C., Brundle, C. R.: Molecular photoelectron spectroscopy. London: Wiley-Interscience 1970
3. Brundle, C. R., Baker, A. D. (eds.): Electron spectroscopy: Theory, techniques and applications, Vol. 1. London: Academic Press 1977
4. Koopmans, T.: Physica 1, 104 (1934); Bock, H.: Angew. Chem. 89, 631 (1977); Angew. Chem. Int. Ed. Engl. 16, 724 (1977)
5. Domcke, W., Cederbaum, L. S., von Niessen, W., Kraemer, W. P.: Chem. Phys. Letters 43, 258 (1976)