title: Anion photoelectron imaging of deprotonated thymine and cytosine.
abstract: We report the anion photoelectron spectra of deprotonated thymine and cytosine at 3.496 eV photodetachment energy using velocity-mapped imaging. The photoelectron spectra of both species exhibit bands resulting from detachment transitions between the anion ground state and the ground state of the neutral radical. Franck-Condon simulations identify the anion isomers that contribute to the observed photoelectron spectrum. For both thymine and cytosine, the photoelectron spectra are consistent with anions formed by removal of a proton from the N atom that normally attaches to the sugar in the nucleotide (N1). For deprotonated thymine, the photoelectron spectrum shows a band due to a ring breathing vibration excited during the photodetachment transition. The electron affinity for the dehydrogenated thymine radical is determined as 3.250 +/- 0.015 eV. For deprotonated cytosine, the photoelectron spectrum lacks any resolved structure and the electron affinity of the dehydrogenated cytosine radical is determined to be 3.037 +/- 0.015 eV. By combining the electron affinity with previously measured gas phase acidities of thymine and cytosine, we determine the bond dissociation energy for the N-H bond that is broken.
authors.affiliation: Department of Chemistry, University of California, Berkeley, CA 94720, USA.
authors.forename: Bradley F
authors.initials: BF
authors.lastname: Parsons
authors.forename: Sean M
authors.initials: SM
authors.lastname: Sheehan
authors.forename: Terry A
authors.initials: TA
authors.lastname: Yen
authors.forename: Daniel M
authors.initials: DM
authors.lastname: Neumark
authors.forename: Nadine
authors.initials: N
authors.lastname: Wehres
authors.forename: Rainer
authors.initials: R
authors.lastname: Weinkauf
mesh_terms: D000577:Amides / Q000737:chemistry; D000838:Anions; D003596:Cytosine / Q000737:chemistry*; D004583:Electrons; D005609:Free Radicals / Q000737:chemistry; D005740:Gases / Q000737:chemistry; D006859:Hydrogen / Q000737:chemistry; D006860:Hydrogen Bonding; D007536:Isomerism; D015394:Molecular Structure; D010777:Photochemistry / Q000379:methods*; D011522:Protons; D013057:Spectrum Analysis / Q000379:methods*; D013941:Thymine / Q000737:chemistry*
chemical_list: D000577:Amides; D000838:Anions; D005609:Free Radicals; D005740:Gases; D011522:Protons; D006859:Hydrogen; D003596:Cytosine; D013941:Thymine