Insights into dynamics of the S2 state of thiophosgene from ab initio calculations

The S-2 potential energy surface for Cl2CS dissociation has been characterized with a combined complete active space self-consistent field and multireference configuration interaction method. The S-3/S-2 minimum-energy intersection has been determined with the state-averaged complete active space self-consistent field method. The S-2 direct dissociation was found to have a barrier of 6.0 kcal/mol, leading to formation of Cl((XP)-P-2)+ClCS(A(2)A(')) in the excited electronic state. Dynamics of the S-2 state of Cl2CS can be summarized as follows: (1) The S-2-S-0 fluorescence occurs with high quantum yield at low excess energies; (2) Both the S-2 dissociation and the S-2-->S-3 internal conversion cause the loss of the S-2-S-0 fluorescence upon photoexcitation at 235-253 nm; (3) The S-2-->S-3 internal conversion (IC) followed by the direct IC to the ground electronic state results in the fragments produced in the ground state, while the S-2 dissociation leads to formation of the fragments in excited electronic states. (C) 2004 American Institute of Physics.