title: Nonadiabatic dynamics of uracil: population split among different decay mechanisms.
abstract: Nonadiabatic dynamics simulations performed at the state-averaged CASSCF method are reported for uracil. Supporting calculations on stationary points and minima on the crossing seams have been performed at the MR-CISD and CASPT2 levels. The dominant mechanism is characterized by relaxation into the S(2) minimum of ππ* character followed by the relaxation to the S(1) minimum of nπ* character. This mechanism contributes to the slower relaxation with a decay constant larger than 1.5 ps, in good agreement with the long time constants experimentally observed. A minor fraction of trajectories decay to the ground state with a time constant of about 0.7 ps, which should be compared to the experimentally observed short constant. The major part of trajectories decaying with this time constant follows the ππ* channel and hops to the ground state via an ethylenic conical intersection. A contribution of the relaxation proceeding via a ring-opening conical intersection was also observed. The existence of these two latter channels together with a reduced long time constant is responsible for a significantly shorter lifetime of uracil compared to that of thymine.
authors.affiliation: Institute of Organic Chemistry and Biochemistry, Flemingovo nám. 2, 166 10 Praha 6, Czech Republic. dana.nachtigallova@uochb.cas.cz
authors.forename: Dana
authors.initials: D
authors.lastname: Nachtigallová
authors.forename: Adélia J A
authors.initials: AJ
authors.lastname: Aquino
authors.forename: Jaroslaw J
authors.initials: JJ
authors.lastname: Szymczak
authors.forename: Mario
authors.initials: M
authors.lastname: Barbatti
authors.forename: Pavel
authors.initials: P
authors.lastname: Hobza
authors.forename: Hans
authors.initials: H
authors.lastname: Lischka
mesh_terms: D056004:Molecular Dynamics Simulation; D011789:Quantum Theory; D014498:Uracil / Q000737:chemistry*
chemical_list: D014498:Uracil