engleski

Dynamic simulations of photodissociations of formamide and its protonated form in the gas phase

Knowledge of how the peptide bond interacts with ultraviolet light has important implications in many fields, to mention only laser surgery and photofragmentation of polymers. In this regard photolysis of formamide and its higher analogons, as the simplest model systems containing peptide bond, have received considerable attention from experimental, as well as from theoretical point of views. In this communication results of our recent computational study of dynamics of photofragmentations of formamide4 and its protonated forms in their low lying no-π * and π – π * states employing the mixed quantum-classical direct trajectory with surface hopping method based on multi-configurational ab initio calculations will be presented. The dynamics simulations for formamide showed that in both states the major deactivation process is C-N bond dissociation, with the decay to the ground state being considerably faster for the (π – π *) state. In addition, in the photofragmentation starting from the π – π *state, alternative deactivation path involving the C-O bond fission was also observed. Similarly, for the O-protonated formamide two deactivation processes were found: the C-N (major) and C-O (minor) dissociation with very short life time (33 fs), whereas the major process for photodecomposition in the first excited state of N-protonated formamide involves the C-N dissociation with a life time of about 390 fs. However, 55% of trajectories remained undissociated and undeactivated until 1000 fs, indicating the exsistence of other deactivation process on a longer time scale.

dynamics simulations; photodissociation; formamide; protonation

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