title: Theoretical study of photoacidity of HCN: the effect of complexation with water.
abstract: The character of the hydrogen bonding and the excited state proton transfer (ESPT) in the model system HCN...H(2)O is investigated. The PES of the two lowest excited states of the H(2)O...HCN 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.
authors.affiliation: Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic and Center for Biomolecules and Complex Molecular Systems, Flemingovo nam. 2, 166 10, Prague 6.
authors.forename: Eva
authors.initials: E
authors.lastname: Muchová
authors.forename: Vladimir
authors.initials: V
authors.lastname: Spirko
authors.forename: Pavel
authors.initials: P
authors.lastname: Hobza
authors.forename: Dana
authors.initials: D
authors.lastname: Nachtigallová
mesh_terms: D003198:Computer Simulation; D006860:Hydrogen Bonding; D006856:Hydrogen Cyanide / Q000737:chemistry*; D008956:Models, Chemical; D010777:Photochemistry; D011522:Protons; D011789:Quantum Theory; D014867:Water / Q000737:chemistry*
chemical_list: D011522:Protons; D014867:Water; D006856:Hydrogen Cyanide