Two- and three-state conical intersections in the uracil cation

The excited states of the uracil radical cation have been studied theoretically using multireference configuration interaction and quasidegenerate perturbation theory methods. The ground state is an 2A″ state and three electronically excited states have been calculated with adiabatic energies 1.00 eV (D1(2A′)), 1.79 eV (D2(2A″)), and 2.31 eV (D3(2A′)). Two-state conical intersections between the ground state D0 and the first excited state D1 have been located 0.45 eV above the ground state minimum. Furthermore, three-state conical intersections between the states D0, D1 and D2 have been located 0.95 eV above the D0 minimum. These conical intersections may play an important role in photoionization processes in uracil.