title: Photodissociation of uracil.
abstract: We investigate the photochemistry and photodissociation dynamics of uracil by two-colour photofragment Doppler spectroscopy and by two-colour slice imaging at excitation wavelengths between 268 and 235 nm. We observe the loss of a hydrogen atom upon excitation into the pipi* state. The angular distribution indicates a statistical process, while the translational energy distribution agrees with a dissociation that takes place on the electronic ground state. The pipi* state most likely deactivates via the lower-lying npi* state. In addition there is evidence for a second pathway: direct decay of the pipi* state to the electronic ground state with subsequent dissociation. Experiments on uracil-1,3-D(2) show that there is no site selectivity in the dissociation process. No evidence was found for the direct dissociation via a pisigma* excited state that seems to be relevant in the photochemistry of adenine and many other heterocyclic molecules. Overall, the photochemistry of uracil is similar to that of thymine.
authors.affiliation: University of Würzburg, Institute of Physical Chemistry, Am Hubland, D-97074, Würzburg, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Schneider
authors.forename: Christof
authors.initials: C
authors.lastname: Schon
authors.forename: Ingo
authors.initials: I
authors.lastname: Fischer
authors.forename: Luis
authors.initials: L
authors.lastname: Rubio-Lago
authors.forename: Theofanis
authors.initials: T
authors.lastname: Kitsopoulos
mesh_terms: D004735:Energy Transfer; D006571:Heterocyclic Compounds / Q000737:chemistry; D007700:Kinetics; D013058:Mass Spectrometry; D010777:Photochemistry; D010782:Photolysis; D013816:Thermodynamics; D013941:Thymine / Q000737:chemistry; D014498:Uracil / Q000737:chemistry*
chemical_list: D006571:Heterocyclic Compounds; D014498:Uracil; D013941:Thymine