An electronic transition described approximately as
promotion of an electron from a '
non-bonding' (lone-pair) n orbital to an '
antibonding '
σ orbital 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 2255