The main features of the ultraviolet spectrum of acrolein have been studied by a multireference perturbative treatment and by a time dependent density functional approach.The valence and Rydberg transition energies have been calculated and the assignment of the experimental bands has been clarified.The different relaxation trends of the three lowest singlet adn triplet excited states have been analyzed by unconsstrained geometry optimizations.This has allowed,in particular,the characterization of a twisted ~3(pipi~*)state,which is crucial for the interesting photophysics and photochemistry of the acrolein molecule and,more generally,of the alpha,beta-enones.Solvatochromic shifts in aqueous solution have been investigated using a combined discrete/continuum approach based on the so called polarizable continuum model.The experimental trends are well reporduced by this approach and a closer degeneracy in the triplet manifold has been detected in solution with respect to gas phase.
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