Regular Article - Topical Issue
Excited state dynamics of protonated keto uracil: intersystem crossing pathways in competition
Université Paris-Saclay, CNRS, Institut des Sciences Moléculaires d’Orsay, 91405, Orsay, France
Accepted: 16 November 2020
Published online: 21 January 2021
The relaxation dynamics of protonated keto uracil has been investigated through cryogenic UV photodissociation spectroscopy. Steady-state spectroscopy and time-resolved photochemistry, including pump-probe photodissociation and kinetics of appearance of photofragments, are monitored over 10 orders of magnitude as a function of excess energy imparted in the bright * state. Although photofragments are produced in the ground electronic state after internal conversion, the non-radiative decay mechanism abruptly changes with a slight increase of excess energy in the * state. At the band origin, a three-step decay involving electronic couplings to the charge transfer * state and the triplet * state with lifetimes in the range of and 2 ms, respectively, is proposed. However, the pathway through the charge transfer state closes a few hundreds of wavenumbers above the band origin. From this excess energy, the excited state population is transferred through a low energy barrier towards a region of the * potential energy surface where a triple crossing with the * state and the ground state is located. The experimental results are assigned with the help of ab initio calculations at the spin-component scaled coupled-cluster level.
© EDP Sciences, SIF and Springer-Verlag GmbH Germany, part of Springer Nature 2021