Theoretical investigation of the mode-specific induced non-radiative decay in 2-pyridone

Experiments on 2-pyridone (2PY) [Y. Matsuda, T. Ebata, N. Mikami, J. Chem. Phys. 113 (2000) 573; J.A. Frey, R. Leist, C. Tanner, H.M. Frey, S. Leutwyler, J. Chem. Phys. 125 (2006) 114308] have revealed that specific vibrational bands in the laser-induced fluorescence spectrum are missing in comparison to the fluorescence depletion spectrum. The possibility of mode-induced non-radiative decay has been raised in order to explain the effect. In the present work, this hypothesis is tested by an extensive investigation of the excited-state energy surfaces of 2PY by means of multireference ab initio methods. Several conical intersections have been located and the paths connecting them to the minimum on the S1 surface have been explored. Mixed quantum-classical dynamics simulations were used to estimate how the bias towards specific modes can modify the non-radiative decay rate. These investigations nicely confirm the proposed mode-induced non-radiative decay mechanism.