Antibonding sigma* orbitals in molecular spectroscopy.

This paper discusses the role of sigma* antibonding valence MO's in the electronic spectra of large molecules. Using the term value and antishielding concepts, molecular absorption patterns terminating at sigma* MO's are systematized and rationalized; the frequencies of such excitations correlate with the ground- state bond strengths of the bonds giving rise to the sigma* MO's. The difference of outer-shell and inner-shell term values, called the antishielding exhaltation, results from an enhanced effective nuclear charge for the optical electron in an inner- shell excitation.