Quintet states of organic molecules: magnetic energies,spin-states and ESR-selection rules

For a pure quintet state (S = 2) consisting of four electrons interacting via magnetic dipole interaction the following magnetic properties are calculated: zero field splitting, selection rules for magnetic dipole transition in zero field, anisotropy of the ESR resonance fields, ESR selection rules and effective spin. The comparison with experimental ESR spectra on intermediate states during the photopolymerisation of diacetylene crystals shows that these states are quintet states.