Nonradiative deactivation of the lowest excited triplet state of the dibenzo-p-dioxin molecule

In the nonadiabatic approximation, we study how intramolecular interactions affect the nonradiative energy degradation T ₁ ^s ↝ S ₀ of triplet sublevels s of the lowest triplet state of the dibenzo-p-dioxin molecule. We consider the role played in the degradation by the shape of promoting high- and low-frequency vibrational modes and by spin-orbit interactions separately in the carbon backbone of the molecule and in heteroatoms (oxygen). We find that σ-electrons of oxygen that correspond to the lone pair and to valence electrons play different roles in the nonadiabatic interaction.