Model and calculation of rate constants of nonradiative <Emphasis Type="Italic">T-S</Emphasis> intersystem conversion: Test by example of naphthalene and its chlorine derivatives

For in-plane spin states (s = z, y), the rate constants K _dg ^s of the nonradiative energy degradation T ₁ ⇝ S ₀ of the lowest triplet T ₁ state of naphthalene (NPH) and its dichloro-substituted derivatives at positions 1,4- and 2,3- of the molecule (1,4-NPH and 2,3-NPH) are calculated. A simple model is proposed for calculations that is based on the nonadiabatic approximation and uses all the out-of-plane vibrational modes of the molecule as promoting vibrational modes. As a result of calculations, the dependences of the rate constants K _dg and K _dg ^s on the positions of chlorine atoms in the molecule are obtained, which are consistent with the known data of magnetooptical measurements. The inversion of the ratio K _dg ^z : K _dg ^y in the 1,4-NPH and 2,3-NPH molecules is established.