An electronic transition described approximately as a
promotion of an electron from a '
bonding' orbital π to an '
antibonding' orbital σ designated as σ*. Such transitions generally involve high transition energies
and appear close to or mixed with
Rydberg transitions.
Source:
PAC, 1996, 68, 2223
(Glossary of terms used in photochemistry (IUPAC Recommendations 1996))
on page 2266