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  • Title: The decay from the dark npi* excited state in uracil: an integrated CASPT2/CASSCF and PCM/TD-DFT study in the gas phase and in water.
    Author: Mercier Y, Santoro F, Reguero M, Improta R.
    Journal: J Phys Chem B; 2008 Sep 04; 112(35):10769-72. PubMed ID: 18700794.
    Abstract:
    By integrating the results of MS-CASPT2/CASSCF and TD-PBE0 calculations, we propose a mechanism for the decay of the excited dark state in pyrimidine, fully consistent with all the available experimental results. An effective conical intersection (CI-npi) exists between the spectroscopic pi/pi* excited state (Spi) and a dark n/pi* state (Sn), and a fraction of the population decays to the minimum of Sn (Sn-min). The conical intersection between Sn and the ground-state is not involved in the decay mechanism, because of its high energy gap with respect to Sn-min. On the other hand, especially in hydrogen bonding solvents, the energy gap between Sn-min and CI-npi is rather small. After thermalization in Sn-min, the system can thus recross CI-npi and then quickly proceed on the Spi barrierless path toward the conical intersection with the ground state.
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