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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 pi pi* character followed by the relaxation to the S(1) minimum of n pi* 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 pi pi* 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.
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Submitted on : Monday, December 12, 2016 - 6:50:38 PM
Last modification on : Wednesday, October 21, 2020 - 3:16:04 PM

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Dana Nachtigallova, Adelia J. A. Aquino, Jaroslaw J. Szymczak, Mario Barbatti, Pavel Hobza, et al.. Nonadiabatic Dynamics of Uracil: Population Split among Different Decay Mechanisms. Journal of Physical Chemistry A, American Chemical Society, 2011, 115 (21), pp.5247--5255. ⟨10.1021/jp201327w⟩. ⟨hal-01415211⟩

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