New Insights into the State Trapping of UV-Excited 2 Thymine 3

International audienceAfter UV excitation, gas phase thymine returns to ground state in 5 to 7 ps, showing 18 multiple time constants. There is no consensus on the assignment of these processes, with a dispute 19 between models claiming that thymine is trapped either in the first (S1) or in the second (S2) excited 20 states. In the present study, nonadiabatic dynamics simulation of thymine is performed on the basis 21 of ADC(2) surfaces, to understand the role of dynamic electron correlation on the deactivation 22 pathways. The results show that trapping in S2 is strongly reduced in comparison to previous 23 simulations considering only non-dynamic electron correlation on CASSCF surfaces. The reason for 24 the difference is traced back to the energetic cost for formation of a CO bond in S2. 2