Uracil, thymine, and adenine anions were produced in charge-exchange collisions with laser-excited Rydberg atoms. Anion creation rates for uracil and thymine exhibit Rydberg electron energy dependences which are interpreted as due to the creation of both dipole-bound and conventional (valence) anions while only dipole-bound anions are observed for adenine.

Articles you may be interested inDecay dynamics of nascent acetonitrile and nitromethane dipole-bound anions produced by intracluster chargetransfer J.Low-energy photoelectron imaging spectroscopy of nitromethane anions: Electron affinity, vibrational features, anisotropies, and the dipole-bound state J. Chem. Phys. 130, 074307 (2009); 10.1063/1.3076892 Dipole bound and valence state coupling in argon-solvated nitromethane anionsConventional ͑valence͒ and dipole-bound anions of the nitromethane molecule are studied using negative ion photoelectron spectroscopy, Rydberg charge exchange and field detachment techniques. Reaction rates for charge exchange between Cs(ns,nd) and Xe(n f ) Rydberg atoms with CH 3 NO 2 exhibit a pronounced maximum at an effective quantum number of n*Ϸ13Ϯ1 which is characteristic of the formation of dipole-bound anions ͓͑CH 3 NO 2 ͒ϭ3.46 D͔. However, the breadth ͑⌬nϷ5, FWHM͒ of the n-dependence of the reaction rate is also interpreted to be indicative of direct attachment into a valence anion state via a ''doorway'' dipole anion state. Studies of the electric field detachment of CH 3 NO 2 Ϫ formed through the Xe(n f ) reactions at various n values provide further evidence for the formation of both a dipole-bound anion as well as a contribution from the valence bound anion. Analysis of the field ionization data yields a dipole electron affinity of 12Ϯ3 meV. Photodetachment of CH 3 NO 2 Ϫ and CD 3 NO 2 Ϫ formed via a supersonic expansion nozzle ion source produces a photoelectron spectrum with a long vibrational progression indicative of a conventional ͑valence bound͒ anion with a substantial difference in the equilibrium structure of the anion and its corresponding neutral. Assignment of the origin ͑vЈϭ0, vЉϭ0͒ transitions in the photoelectron spectra of CH 3 NO 2 Ϫ and CD 3 NO 2 Ϫ yields adiabatic electron affinities of 0.26Ϯ0.08 and 0.24Ϯ0.08 eV, respectively.

At the very early time of irradiation, ballistic secondary electrons are produced as the most abundant of the radiolytic species directly within DNA or its environment. Here, we demonstrate the propensity of such low-energy (<3 eV) electrons to damage DNA bases via an effective loss of hydrogen located at the specific nitrogen positions. Since this site is directly implicated in the bonding of nucleobases within DNA and since dehydrogenation of the nucleic acid bases has been observed to be the predominant dissociative channel, the present findings foreshadow significant implications for the initial molecular processes leading to genotoxicity in living cells following unwanted or intended exposure to ionizing radiation (e.g., sunbathing, air travel, radiotherapy, etc.).

Ground-state dipole-bound anions are fragile molecular species which excess electrons are almost entirely located in a very diffuse orbital outside the molecular frame. They can be created by attachment of very low energy electrons to polar molecules or small clusters which dipole moments are larger than a practical critical value of 2.5 D. They present analogies with Rydberg atoms and their geometrical structures are nearly identical to those of their neutral parents. Experimentally, dipole-binding of electrons to polar systems is a non-perturbative and reversible ionization process, in contrast with conventional valence-binding. Examples of applications such as mass-spectrometric isomer selection of clusters or determination of electron attachment properties of isolated nucleic acid bases are given.

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