Response theory calculations of the singlet-triplet transition probabilities in the HOCl molecule

The role of the HOCl molecule in stratospheric photochemistry is highly dependent on its photolysis in the long wavelength region (λ ≥ 300 nm). In order to predict the possible importance of the singlet-triplet absorption in this molecule we have performed geometry optimizations of the ground singlet X¹ A′ and the excited triplet ³A″ and ³A′ states, and performed quadratic response theory calculations of the singlet-triplet transition probabilities at different bending angles and O-Cl distances, accounting for the complete form of the spin-orbit coupling operator. Based on the results of these calculations the importance of the ³A″ ← X¹ A′ and ³A′ ← X¹ A′ absorption in HOCl photolysis is discussed.