Simulation of optical spectra and phenolic compound photolysis
V.A. Pomogaev1,2, O.N. Tchaikovskaya1,3
1National Research Tomsk State University, Tomsk, Russia
2Saint-Petersburg State University, Institute of Chemistry, St. Petersburg, Russia
3Institute of Electrophysics of the Ural Division of the Russian Academy of Sciences, Ekaterinburg, Russia
Keywords: phenol, vanillin, p-cresol, electronic transitions, static optical spectra, conical intersection, nonadiabatic photochemistry
Abstract
Phenol enters the environment during the combustion of plants and biomass, as well as through anthropogenic emissions. Phenolic compounds can act as precursors to organic aerosols, adversely affects human health, and reduces atmospheric visibility. The static absorption spectra of phenol and its volatile substituted compounds ( p-cresol and vanillin) presented in this work were obtained and analyzed using computer simulations based on quantum-mechanical molecular dynamics. The optical spectra were averaged over excited instantaneous molecular conformers fluctuating along system's evolution trajectories. The photodynamic dissipation of electronically excited states of the molecules was studied by generating trajectories in nonadiabatic molecular dynamics. Changes in the electronic structure of phenol, p-cresol, and vanillin, along with the crossing points and dissociation of potential energy surfaces, were obtained using the mixed-reference spin-flip approach within the time-dependent density functional theory. The O-H bond breaking in the hydroxyl group followed by deprotonation causes minor structural deformations for the molecules under study. It is shown that, upon excitation, the dissociation of the hydroxyl group occurs via an electronic transition to the σ-MO localized on the elongated O-H bond.
|
