Photoelectron spectrum and dynamics of the uracil cation.

The photoelectron spectrum of uracil and the molecular dynamics of its radical cation are investigated using the multiconfigurational time-dependent Hartree (MCTDH) method. For this aim, the vibronic coupling model Hamiltonian is used including up to ten important a' modes. Moreover, to account for coupling through conical intersections between states of different symmetry in the system, coupling constants of two a″ modes are taken into account. The parameters used in the model are obtained by fitting to ab inito data obtained with extensive EOM-IP-CCSD calculations. The first four cationic states were investigated, which are either of A″ (hole in a π orbital) or A' (hole in a nO orbital) symmetry. The results of the wavepacket propagations were used to calculate the corresponding photoelectron spectrum and compare to the experimental spectrum. The MCTDH simulations reproduce the experimental spectrum well. The dynamics starting from the D2 and D3 ionic states show a fast relaxation to the cationic ground state often involving direct D2-D0 or D3-D1 transitions.