An electronic transition described approximately as @P04877@ of an electron from a 'bonding' orbital to a @R05431@. Spectral bands corresponding to Rydberg transitions approximately fit the Rydberg formula: \[\sigma = I - \frac{R}{(n\,-\,\mathit{\Delta })^{2}}\] where \(\sigma \) is the wavenumber, \(I\) the @I03208@ of the atom or molecular entity, \(n\) a principal quantum number, \(R\) the @R05430@, and \(\mathit{\Delta}\) the quantum defect which differentiates between s, p, d, etc., orbitals. The notation used is, e.g. \(\pi \rightarrow \mathrm{ns}\).