Theoretical Study of Photoacidity of HCN: the Effect of Complexation with Water.
Muchova, E.; Spirko, V.; Hobza, P. etc.,
Physical Chemistry Chemical Physics, 8 4866 - 4873 (2006)
The character of the hydrogen bonding and the excited state proton transfer (ESPT) in the model system (HCNH2O)-H-... is investigated. The PES of the two lowest excited states of the (H2OHCN)-H-... complex was calculated using the CASPT2 method. The nonadiabatic coupling of the two states of the (pi -> pi *) and (pi -> sigma*) character is responsible for the excited state proton/hydrogen transfer. Compared to the ground state, the barrier for this process is significantly smaller. An increased number of water molecules in the complex with cyclic hydrogen-bonded network causes a large blue shift of the state of the (pi -> sigma*) character. The question of the dissociation of the complex in its excited state is also addressed.