Nonadiabatic dynamics of uracil: Population split among different decay mechanisms

Dana Nachtigallovaí, Adélia J.A. Aquino, Jaroslaw J. Szymczak, Mario Barbatti, Pavel Hobza, Hans Lischka

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80 Scopus citations


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 S1 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.

Original languageEnglish
Pages (from-to)5247-5255
Number of pages9
JournalJournal of Physical Chemistry A
Issue number21
StatePublished - Jun 2 2011


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