Sascha Gohlke

Dissociative electron attachment to furan, tetrahydrofuran, and fructose

We study dissociative electron attachment to furan (FN) (C(4)H(4)O), tetrahydrofuran (THF) (C(4)H(8)O), and fructose (FRU) (C(6)H(12)O(6)) using crossed electron/molecular beams experiments with mass spectrometric detection of the anions. We find that FN and THF are weak electron scavengers and subjected to dissociative electron attachment essentially in the energy range above 5.5 eV via core excited resonances. In striking contrast to that, FRU is very sensitive towards low energy electrons generating a variety of fragment ions via a pronounced low energy feature close to 0 eV. These reactions are associated with the degradation of the ring structure and demonstrate that THF cannot be used as surrogate to model deoxyribose in DNA with respect to the attack of electrons at subexcitation energies (<3 eV). The results support the picture that in DNA the sugar moiety itself is an active part in the initial molecular processes leading to single strand breaks.

Formation of anion fragments from gas-phase glycine by low energy (0–15 eV) electron impact

We have measured the formation of anion fragments in gas phase glycine (H2NCH2COOH) via dissociative electron attachment (DEA) reactions in the 0–15 eV electron energy range, using a monochromatic electron beam and mass spectrometric detection of the negative ions. By far the most intense product observed is the closed shell glycine anion (H2NCH2COO)− which appears from a low-energy resonance with a peak located at 1.4 eV and a cross section in the range 10−16 cm2. The corresponding precursor ion can be characterized by electron attachment into the empty π* orbital of the −COOH group as recently assigned from electron transmission experiments and ab initio self-consistent field calculations [Aflatooni, Hitt, Gallup, and Burrow, J. Chem. Phys. 115, 6489 (2001)]. This precursor state is also observed to decompose (with much lower intensity) yielding a negative ion fragment with 58 amu, which is attributed to anions of the stoichiometric composition H2C2O2− or H4C2NO−. A further prominent DEA peak is observe...

Conversion of amino-acids by electrons at subexcitation energies

Electron attachment to gas phase cysteine is investigated in a crossed electron/molecular beam experiment. The yield functions of the detected anions exhibit signatures of dissociative electron attachment (DEA), initiated by shape ( 5 eV) resonances. These parent anion precursor states decompose into a variety of negatively charged fragments with one of the most dominant channels being dehydrogenation, i.e., abstraction of the H radical with the excess electron remaining on the cysteine-like moiety. While this reaction is operative only within the low energy range, S− and SH− appear from both resonance regions. From energy considerations it is shown that formation of S− below 3 eV must be associated with a conversion of cysteine into alanine. The present results demonstrate the capacity of electrons at subexcitation energies to effectively change the nature of amino acids.

A study of dissociative electron attachment to CHBr3 and CHI3

Dissociative electron attachment (DEA) has been studied in the systems Br−/CHBr3 and I−/CHI3 in a crossed electron/molecular beams experiment in the electron energy range from about 0 to 10 eV. In addition to prominent low-energy resonances (also observed in previous studies), we find a resonance in the system Br−/CHBr3 at 4.65 eV and we find three additional resonant features in the system I−/CHI3 at 2.1, 2.9 and 4.1 eV. The absolute partial cross-section for the Br−/CHBr3 DEA reaction was estimated as (3 ± 1) × 10−17 cm2 at 0.5 eV and (2 ± 1) × 10−18 cm2 at 4.65 eV. Analysis of the energy dependence of the I−/CHI3 cross-section reveals s-wave attachment near threshold (≈0 eV) and an additional pronounced feature located at 58 meV. We tentatively assign this feature to vibrational Feshbach resonance associated with excitation of the ν2 vibrational quanta of CHI3.

Electron Attachment to Biologically Relevant Molecules: Towards the Initial Molecular Steps in Radiation Damage

The interaction of low energy electrons with biomolecules is directly related to the old problem of radiation damage. After the discovery of X-rays, radioactivity and nuclear fission it became soon obvious that the exposure of living beings to high energy radiation (particles and photons) can result in fatal effects for the concerned individual. The variety of such effects is subsumed under the term radiation damage. It includes damage of biological material on a short time scale, i.e. the immediate collapse of living cells eventually resulting in the death of the individual within hours or days but also effects appearing on a much longer time scale. Instead of a complete damage of cells, radiation can result in genotoxic or mutagenic effects, i. e. strand breaks in DNA or change of its sequence (genetic expression).