Intramolecular vibrational redistribution in the non-radiative excited state decay of uracil in the gas phase: an ab initio molecular dynamics study

摘要: We report a study of intramolecular vibrational distribution (IVR) occurring in the electronic ground state uracil (S0) gas phase, following photoexcitation lowest energy bright excited (Sπ) and decay through ethylene-like Sπ/S0 Conical Intersection (CI-0π). To this aim we have performed 20 independent ab initio molecular dynamics simulations starting from CI-0π (ten them with 1 eV kinetic randomly distributed over different degrees freedom) 10 minimum (Franck–Condon, FC, point), excess equal to gap between FC point. The simulations, exploiting PBE0/6-31G(d) calculations, were an overall period ps. A thorough statistical analysis variation geometrical parameters during simulation time among freedom provides consistent picture IVR process. In first 0–200 fs structural involve mainly recovery average planarity. 200–600 range, substantial activation CO NH is observed. After 500–600 most reach values similar those found after ps, though system cannot be considered equilibrium yet.