title: On the relaxation mechanisms of 6-azauracil.
abstract: The nonadiabatic photochemistry of 6-azauracil has been studied by means of the CASPT2//CASSCF protocol and double-ζ plus polarization ANO basis sets. Minimum energy states, transition states, minimum energy paths, and surface intersections have been computed in order to obtain an accurate description of several potential energy hypersurfaces. It is concluded that, after absorption of ultraviolet radiation (248 nm), two main relaxation mechanisms may occur, via which the lowest (3)(ππ*) state can be populated. The first one takes place via a conical intersection involving the bright (1)(ππ*) and the lowest (1)(nπ*) states, ((1)ππ*/(1)nπ*)(CI), from which a low-energy singlet-triplet crossing, ((1)nπ*/(3)ππ*)(STC), connecting the (1)(nπ*) state to the lowest (3)(ππ*) triplet state is accessible. The second mechanism arises via a singlet-triplet crossing, ((1)ππ*/(3)nπ*)(STC), leading to a conical intersection in the triplet manifold, ((3)nπ*/(3)ππ*)(CI), evolving to the lowest (3)(ππ*) state. Further radiationless decay to the ground state is possible through a (gs/(3)ππ*)(STC).
authors.affiliation: Instituto de Química, Universidade de São Paulo, Av. Prof. Lineu Prestes, 748, 05508-900, São Paulo, SP, Brazil.
authors.forename: João Paulo
authors.initials: JP
authors.lastname: Gobbo
authors.forename: Antonio Carlos
authors.initials: AC
authors.lastname: Borin
authors.forename: Luis
authors.initials: L
authors.lastname: Serrano-Andrés
mesh_terms: D011789:Quantum Theory; D013816:Thermodynamics; D014498:Uracil / Q000031:analogs & derivatives* / Q000737:chemistry
chemical_list: D014498:Uracil; C100248:azauracil