title: Tautomerism in cytosine and uracil: a theoretical and experimental X-ray absorption and resonant auger study.
abstract: The core level photoabsorption spectra of the nucleobases cytosine and uracil in the gas phase have been measured and the results interpreted with theoretical calculations using an ab initio Green’s function approach. A single tautomer of uracil is populated, in agreement with previous work, while three tautomers of cytosine are clearly identified, whose identity and relative populations at the temperature of the experiment were reported previously. The second-order ADC approach to polarization propagator was employed in calculations of X-ray photoabsorption energies and intensities. The theoretical spectra have been constructed as Boltzmann-factor-weighted sums of individual tautomer spectra. These theoretical spectra are in good agreement with the experimental photoabsorption results at the oxygen, nitrogen, and carbon edges. In addition we report resonant Auger spectra of the valence band of cytosine, which support previous assignments of the character of the valence band states.
authors.affiliation: Sincrotrone Trieste, in Area Science Park, I-34012 Basovizza (Trieste), Italy.
authors.forename: Vitaliy
authors.initials: V
authors.lastname: Feyer
authors.forename: Oksana
authors.initials: O
authors.lastname: Plekan
authors.forename: Robert
authors.initials: R
authors.lastname: Richter
authors.forename: Marcello
authors.initials: M
authors.lastname: Coreno
authors.forename: Monica
authors.initials: M
authors.lastname: de Simone
authors.forename: Kevin C
authors.initials: KC
authors.lastname: Prince
authors.forename: Alexander B
authors.initials: AB
authors.lastname: Trofimov
authors.forename: Irina L
authors.initials: IL
authors.lastname: Zaytseva
authors.forename: Jochen
authors.initials: J
authors.lastname: Schirmer
mesh_terms: D003596:Cytosine / Q000737:chemistry*; D056004:Molecular Dynamics Simulation; D010777:Photochemistry; D011789:Quantum Theory; D014498:Uracil / Q000737:chemistry*; D056928:X-Ray Absorption Spectroscopy; D014965:X-Rays
chemical_list: D014498:Uracil; D003596:Cytosine