title: Are conical intersections responsible for the ultrafast processes of adenine, protonated adenine, and the corresponding nucleosides?
abstract: Excited-state potential energy surfaces of adenine, protonated adenine, and their N9-methylated analogs are explored by means of a complete active space (CAS) and time-dependent density functional theory (TD-DFT) study to understand the dynamics associated with internal conversion. After photoexcitation of the ground-state molecules to the S(1) state, the nuclear motions that are responsible for taking the wavepacket out of the Franck-Condon region are either an H--N9/C--N9 stretch or a ring-puckering motion that leads to pyramidalization. These motions lead to accessible conical intersections with the ground-state surface. The results are used to successfully interpret previous measurements on the photodissociation of adenosine 5'-monophosphate nucleotide anions and cations, where the latter react in a highly nonstatistical manner.
authors.affiliation: Department of Physics and Astronomy, University of Aarhus, 8000 Aarhus C, Denmark.
authors.forename: Steen
authors.initials: S
authors.lastname: Brøndsted Nielsen
authors.forename: Theis I
authors.initials: TI
authors.lastname: Sølling
mesh_terms: D000225:Adenine / Q000031:analogs & derivatives / Q000737:chemistry*; D008956:Models, Chemical; D009705:Nucleosides / Q000737:chemistry*; D010777:Photochemistry; D011789:Quantum Theory; D013499:Surface Properties; D013997:Time Factors
chemical_list: D009705:Nucleosides; D000225:Adenine