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.
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.
Mercier
Yannick
Y
Department de Quimica Fisica i Inorganica, Universitat Rovira i Virgili, Marcel.li Domingo, s/n-Campus Sescelades, 43007 Tarragona, Spain.
Santoro
Fabrizio
F
Reguero
Mar
M
Improta
Roberto
R
D004583:Electrons; D005740:Gases / Q000737:chemistry*; D011789:Quantum Theory; D013499:Surface Properties; D014498:Uracil / Q000737:chemistry*; D014867:Water / Q000737:chemistry*
D005740:Gases; D014867:Water; D014498:Uracil