Theory of n to π* Transitions

The Pariser—Parr—Popple (PPP) theory of conjugated systems is extended to take into account non‐bonding orbitals. We show that the ${\mathrm{n\to \pi }}^{*}$ transition gives rise to a Franck—Condon overlap analog of a Fermi π‐electron system. A model calculation for pyridine is presented.