title: Three-state conical intersections in nucleic acid bases.
abstract: The involvement of three-state conical intersections in the photophysics and radiationless decay processes of the nucleobases has been investigated using multireference configuration interaction methods. Three-state conical intersections have been located for the pyrimidine base, uracil, and the purine base, adenine. In uracil, a three-state degeneracy between the S(0), S(1), and S(2) states has been located at 6.2 eV above the ground-state minimum energy. This energy is 0.4 eV higher than vertical excitation to S(2) and at least 1.3 eV higher than the two-state conical intersections found previously. In adenine, two different three-state degeneracies between the S(1), S(2), and S(3) states have been located at energies close to the vertical excitation energies. The energetics of these three-state conical intersections suggest they can play a role in a radiationless decay pathway present in adenine. The existence of two different seams of three-state conical intersections indicates that these features are common and complicate the potential energy surfaces of adenine and possibly many other aromatic molecules.
authors.affiliation: Department of Chemistry, Temple University, Philadelphia, PA 19122, USA. smatsika@temple.edu
authors.forename: Spiridoula
authors.initials: S
authors.lastname: Matsika
mesh_terms: D000225:Adenine / Q000737:chemistry*; D008956:Models, Chemical; D015394:Molecular Structure; D009696:Nucleic Acids / Q000737:chemistry*; D014498:Uracil / Q000737:chemistry*
chemical_list: D009696:Nucleic Acids; D014498:Uracil; D000225:Adenine