Low energy electron attachment to condensed formic acid

Dissociative electron attachment to formic acid in the condensed phase is studied using improved mass spectrometric detection of the negative ion fragments. The desorbed yields are measured as a function of incident electron energy in the range between 3 to 20 eV. Unlike previous work, the formation of the dehydrogenated anion HCOO? is observed and the signal to noise ratio is much higher for all other ions detected, i.e. OH?, O? and H?. Resonant structure seen in all anion yield functions, is attributed to dissociative electron attachment (DEA), whereas above 14 eV nonresonant dipolar dissociation (DD) dominates the desorption yields

Electron Transmission Spectroscopy in Atomic Hydrogen

An electron transmission experiment is used to study the resonances in the total scattering cross section of atomic hydrogen below the threshold of the first excited state. The three lowest resonances, designated 1S, 3P, and 1D, are observed and their energies and decay widths are found to be in good agreement with the values predicted theoretically using close coupling with correlation

Electron Transmission Spectroscopy in Atomic Hydrogen

An electron transmission experiment is used to study the resonances in the total scattering cross section of atomic hydrogen below the threshold of the first excited state. The three lowest resonances, designated 1S, 3P, and 1D, are observed and their energies and decay widths are found to be in good agreement with the values predicted theoretically using close coupling with correlation

Low-energy electron diffraction and resonances in DNA and other helical macromolecules

We propose a framework to calculate the intermolecular multiple elastic scattering of low-energy electrons from helical macromolecules and indicate how it affects the resonant capture cross section. Using a model of DNA, an appreciable enhancement of the elastic and resonant capture cross sections is predicted at incident energies below 15 eV. These results may qualitatively explain the observed prominence of low-energy resonances in strand breaking of plasmid DNA. DOI: 10.1103/PhysRevLett.91.113201 PACS numbers: 34.80.Bm, 87.64.Bx Recent technological advances have rendered possible measurements of low-energy electron scattering and attachment processes in large biological molecules such as DNA Even though reasonably successful theories have been proposed to explain the behavior of electron-molecule scattering at low energies, no suitable framework presently exists to treat the scattering problem with a molecule that may contain up to 10 10 atoms. As such this number is too large for a solution with density functional theory In this paper, we first address the multiple scattering problem and then attempt to connect it to local resonant capture. In a helical macromolecule, such as DNA, the angular twist in the sequence of rungs (the base pairs of DNA and their sugar-phosphate partners) is a fundamental geometrical property which is of crucial importance to the diffraction process. We thus propose a study of the interference produced by a helical structure. We show that with the present formulation, the energy dependence of the electron wave function inside DNA and similar helical macromolecules can be obtained with minimal computer time, and the diffraction of the electron wave may explain qualitatively the large contribution of electron resonances to DNA damage below 15 eV. We propose a simple model of molecular subunits (i.e., bases, sugars, and phosphates) immersed in an optical potential U op , which is constant between their R-matrix shells, a working hypothesis used in the calculations for simple molecule

Diffraction in low-energy electron scattering from DNA: bridging gas phase and solid state theory

Using high-quality gas phase electron scattering calculations and multiple scattering theory, we attempt to gain insights on the radiation damage to DNA induced by secondary low-energy electrons in the condensed phase, and to bridge the existing gap with the gas phase theory and experiments. The origin of different resonant features (arising from single molecules or diffraction) is discussed and the calculations are compared to existing experiments in thin films.Comment: 40 pages preprint, 12 figures, submitted to J. Chem. Phy

X-ray induced damage in DNA monitored by X-ray photoelectron spectroscopy

In this work, the chemical changes in calf thymus DNA samples were analyzed by X-ray photoelectron spectroscopy XPS. The DNA samples were irradiated for over 5 h and spectra were taken repeatedly every 30 min. In this approach the X-ray beam both damages and probes the samples. In most cases, XPS spectra have complex shapes due to contributions of C, N, and O atoms bonded at several different sites. We show that from a comparative analysis of the modification in XPS line shapes of the C 1s, O 1s, N 1s, and P 2p peaks, one can gain insight into a number of reaction pathways leading to radiation damage to DNA

Near-threshold electron transfer in anion-nucleobase clusters : Does the identity of the anion matter?

Laser dissociation spectroscopy of I − ·adenine (I − ·A) and H 2 PO − 3 ·adenine (H 2 PO − 3 ·A) has been utilised for the first time to explore how the anion identity impacts on the excited states. Despite strong photodepletion, ionic photofragmentation is weak for both clusters, revealing that they decay predominantly by electron detachment. The spectra of I − ·A display a prominent dipole-bound excited state in the region of the detachment energy which relaxes to produce deprotonated adenine. In contrast, near-threshold photoexcitation of H 2 PO − 3 ·A does not access a dipole-bound state, but instead displays photofragmentation properties associated with ultrafast decay of an adenine-localised π→π* transition. Notably, the experimental electron detachment onset of H 2 PO − 3 ·A is around 4.7 eV, which is substantially lower than the expected detachment energy of an ion-dipole complex. The low value for H 2 PO − 3 ·A can be traced to initial ionisation of the adenine followed by significant geometric rearrangement on the neutral surface. We conclude that these dynamics quench access to a dipole-bound excited state for H 2 PO − 3 ·A and subsequent electron transfer. H 2 PO − 3 ·A represents an important new example of an ionic cluster where ionisation occurs from the neutral cluster component and where photodetachment initiates intra-molecular hydrogen atom transfer

Communication: Site-selective bond excision of adenine upon electron transfer

This work demonstrates that selective excision of hydrogen atoms at a particular site of the DNA base adenine can be achieved in collisions with electronegative atoms by controlling the impact energy. The result is based on analysing the time-of-flight mass spectra yields of potassium collisions with a series of labeled adenine derivatives. The production of dehydrogenated parent anions is consistent with neutral H loss either from selective breaking of C–H or N–H bonds. These unprecedented results open up a new methodology in charge transfer collisions that can initiate selective reactivity as a key process in chemical reactions that are dominant in different areas of science and technology

Dissociative electron attachment to the H2O molecule. I. Complex-valued potential-energy surfaces for the 2B1, 2A1, and 2B2 metastable states of the water anion

We present the results of calculations defining global, three-dimensional representations of the complex-valued potential-energy surfaces of the doublet B1, doublet A1, and doublet B2 metastable states of the water anion that underlie the physical process of dissociative electron attachment to water. The real part of the resonance energies is obtained from configuration-interaction calculations performed in a restricted Hilbert space, while the imaginary part of the energies (the widths) is derived from complex Kohn scattering calculations. A diabatization is performed on the 2A1 and 2B2 surfaces, due to the presence of a conical intersection between them. We discuss the implications that the shapes of the constructed potential-energy surfaces will have upon the nuclear dynamics of dissociative electron attachment to H2O. This work originally appeared as Phys Rev A 75, 012710 (2007). Typesetting errors in the published version have been corrected here.Comment: Corrected version of PRA 75, 012710 (2007