Theory of two coupled triplet states

Abstract

We present a theory of the magnetic dipolar interaction of two electrostatically coupled carbene triplet states. Using a model spin hamiltonian of a bicarbene system the spin functions and energy eigenvalues of the singlet (S = 0), triplet (S = 1), quintet (S = 2) and mixed singlet-quintet spin pair states are calculated. The resulting zero field and high field E.S.R. spectra are sensitively dependent on the energy separation Δ_εSQ resulting from different electronic configurations of the same symmetry between the individual total singlet and quintet spin pair states. The results of this theory are compared with the E.S.R. data of the quintet states observed during low temperature photopolymerization of diacetylene single crystals.