Theoretical investigation of the electronic spectrum of pyrazine

The electronic spectrum of pyrazine has been the subject of several experimental and theoretical studies. This molecule has for a long time been of interest not only because it provides insight into the molecular dynamics of simple aromatic systems but also because it is a fundamental parent system for numerous biologically active compounds such as nicotinic acid and the nucleotides cytosine, uracil, and thymine, etc. By using CASSCF and CASPT2 methods we have already presented an article (accepted to TCA) to find a suitable basis set and active space not only for the description of valence excited states but also of Rydberg states. The interaction of the first and second excited singlet states (S1 and S2) of pyrazine is a prominent example for vi bronic coupling and has therefore been investigated in detail by experimentalists and theoreticians. However, much less is known about the higher lying singlet states, which include valence as well as Rydberg states. The goal of this project is an impro ved understanding of the nature of the higher energy part of the electronic spectrum of pyrazine beyond the S1 and S2 bands, in particular with respect to vibronic interactions between the various states. Using our experience obtained on this system we w ould like to extend our studies in order to calculate very accurately potential energy surfaces for higher lying excited states, localizing conical intersections between the S1 and S2 bands, in particular with respect to vibronic interactions between the various states. Using our experience obtained on this system we would like to extend our studies in order to calculate very accurately potential energy surface for higher lying excited states, localizing conical intersections between them and eventually to perform dynamical calculations.