Dynamics Of Dissociative Electron Attachment Research Articles

Dynamics of dissociative electron attachment to aliphatic thiols.

Dissociative electron attachment (DEA) shows functional group-dependent site selectivity in H- ion channels. In this context, thiol functional groups have yet to be studied in great detail, although they carry importance in radiation damage studies where low-energy secondary electrons are known to induce damage through the DEA process. In this context, we report detailed measurements of absolute cross-sections and momentum images of various anion fragments formed in the DEA process in simple aliphatic thiols. We also compare the observed dynamics with that reported earlier in hydrogen sulphide, the precursor molecule for this functional group, and with that in aliphatic alcohols. Our findings show substantial resemblance in the underlying dynamics in these compounds and point to a possible generalisation of these features in the DEA to thiols. In addition, we identify various pathways that contribute to the S- and SH- channels.

Dissociative electron attachment to carbon dioxide

Our experimental progresses on the reaction dynamics of dissociative electron attachment (DEA) to carbon dioxide (CO2) are summarized in this review. First, we introduce some fundamentals about the DEA dynamics and provide an epitome about the DEAs to CO2. Second, the experimental technique developments are described, in particular, on the high-resolution velocity map imaging apparatus in which we put a lot of efforts during the past two years. Third, our findings about the DEA dynamics of CO2 are surveyed and briefly compared with the others’ work. At last, we give a perspective about the applications of the DEA studies and highlight the inspirations in the production of molecular oxygen on Mars and the catalytic transformations of CO2.

Selective bond-breaking in formic acid by dissociative electron attachment.

We report the results of a joint experimental and theoretical study of dissociative electron attachment to formic acid (HCOOH) in the 6-9 eV region, where H- fragment ions are a dominant product. Breaking of the C-H and O-H bonds is distinguished experimentally by deuteration of either site. We show that in this region H- ions can be produced by formation of two or possibly three Feshbach resonance (doubly-excited anion) states, one of which leads to either C-H or O-H bond scission, while the other can only produce formyloxyl radicals by O-H bond scission. Comparison of experimental and theoretical angular distributions of the anion fragment allows the elucidation of state specific pathways to dissociation.

Dissociative electron attachment to polyatomic molecules

Dissociative electron attachment (DEA) to molecule plays a key role in atmosphere, interstellar space and ionization damages of biological tissue. Experimental DEA studies of polyatomic molecules in gas phase provide the dynamics details that are the fundamentals to establish the physicochemical models of the electron-induced reactions in complicated environments. Since 2012, we successively set up two ion-velocity-map-imaging apparatuses, and accomplished a series of experimental studies of the DEA dynamics. Here is a brief review about our progresses on polyatomic molecules.

Dissociation dynamics of transient anion formed via electron attachment to sulfur dioxide.

We report the molecular dynamics of dissociative electron attachment to sulfur dioxide (SO2) by measuring the momentum distribution of fragment anions using the velocity slice imaging technique in the electron energy range of 2-10 eV. The S- channel results from symmetric dissociation which exhibits competition between the stretch mode and bending mode of vibration in the excited parent anion. The asymmetric dissociation of parent anions leads to the production of O- and SO- channels where the corresponding neutral fragments are formed in their ground as well as excited electronic states. We also identify that internal excitation of SO- is responsible for its low yield at higher electron energies.

Dissociation dynamics of transient anion formed via electron attachment to sulphur dioxide (SO2)

SynopsisWe have investigated the dynamics of dissociative electron attachment to sulfur dioxide (SO2) using velocity slice imaging (VSI) technique. The symmetric dissociation of the transient parent anion results in S− formation whereas its asymmetric dissociation results in the O− and SO− channels. We clearly see the competition between bending and stretch mode of vibrations of the parent anions in S− formation whereas the stretch modes dominate in the other two ions production.

Dynamics of dissociative electron attachment to ammonia

A joint experimental and theoretical study on dissociative electron attachment to ammonia molecules has identified Feshbach states responsible for the two principal breakup channels observed decades ago. The insight obtained reveals rich collisional dynamics that lead to a breakdown of the axial recoil approximation and to mirror images of the angular distributions in the breakup channels.

Use of heavy-Rydberg ion-pair states to probe dissociative electron attachment

Electron transfer in collisions between Rydberg atoms and targets that attach free low-energy electrons can lead to the formation of heavy-Rydberg ion-pair states comprising a positive-negative ion pair that orbit each other at large separations weakly bound by their mutual electrostatic attraction. It is shown that measurements of the velocity distribution of the ion-pair states produced in such collisions provide a novel probe of the dynamics of dissociative electron attachment.

Use of heavy-Rydberg ion-pair states to probe dissociative electron attachment

SynopsisMeasurements of the velocity distributions of heavy Rydberg ion-pair states formed through electron transfer in collisions between Rydberg atoms and attaching targets are used to probe the dynamics of dissociative electron attachment.

Dissociation dynamics in the dissociative electron attachment to carbon dioxide

Dissociative electron attachment (DEA) to gas phase ${\mathrm{CO}}_{2}$ has been probed using a velocity slice imaging technique. DEA to ${\mathrm{CO}}_{2}$ produces only an ${\mathrm{O}}^{\ensuremath{-}}$ ionic fragment and shows two major resonances located at 4.4 and 8.2 eV, respectively. The kinetic energy and angular distribution of the ${\mathrm{O}}^{\ensuremath{-}}$ ions are measured around the second resonance with higher efficiency and sensitivity that provide details of the DEA dynamics. The kinetic energy distributions are in good agreement with the previous reports. However, the distinct angular distributions show substantial difference from the two recent studies within the limited electron energies. Our angular distribution results show two negative ion resonant states are involved in the underlying DEA process at the entire electron energies over the second resonance. We discussed the recent conflicting findings in the angular distribution results. The forward-backward asymmetry observed in the angular distributions is explained due to the interference effect of different partial waves associated with the attaching electron.

Dissociative electron attachment studies on acetone.

Dissociative electron attachment (DEA) to acetone is studied in terms of the absolute cross section for various fragment channels in the electron energy range of 0-20 eV. H(-) is found to be the most dominant fragment followed by O(-) and OH(-) with only one resonance peak between 8 and 9 eV. The DEA dynamics is studied by measuring the angular distribution and kinetic energy distribution of fragment anions using Velocity Slice Imaging technique. The kinetic energy and angular distribution of H(-) and O(-) fragments suggest a many body break-up for the lone resonance observed. The ab initio calculations show that electron is captured in the multi-centered anti-bonding molecular orbital which would lead to a many body break-up of the resonance.

Dynamics of the Dissociating Uracil Anion Following Resonant Electron Attachment.

We report a combined experimental and theoretical investigation of dissociative electron attachment (DEA) to the nucleobase uracil. Using ion momentum imaging experiments employing a DEA reaction microscope we have measured 3-dimensional momentum distributions of specific anionic fragments following DEA to uracil by 6 eV electrons. From the measured anion fragment kinetic energy we determine the possible dissociation pathways and the total kinetic energy release. We employ electronic structure and electron scattering calculations to determine the probability for electron attachment in the molecular frame. Combining these calculations with the imaging measurements, we reveal several key features of the coupled electronic and nuclear dynamics of DEA.

Dynamical Studies of Dissociative Electron Attachment to CO2

We report the results of our combined experimental and theoretical investigation on the dynamics of dissociative electron attachment to the triatomic molecule CO2. The experiments employ a 4π momentum spectrometer to collect kinematically complete data for this 2-body dissociation reaction. The angular dependence of the attachment entrance amplitudes, calculated by ab initio methods, connect the laboratory frame to the molecular frame. Preliminary results from our ongoing investigations of DEA to larger molecules, including formic acid and the nucleobases uracil and and thymine, will also be presented.

Comment on “Imaging the Molecular Dynamics of Dissociative Electron Attachment to Water”

A Comment on the Letter by H. Adaniya et al., Phys. Rev. Lett. 103, 233201 (2009). The authors of the Letter offer a Reply.

Imaging the Molecular Dynamics of Dissociative Electron Attachment to Water

Momentum imaging experiments on dissociative electron attachment (DEA) to a water molecule are combined with ab initio theoretical calculations of the angular dependence of the quantum mechanical amplitude for electron attachment to provide a detailed picture of the molecular dynamics of dissociation attachment via the two lowest energy Feshbach resonances. The combination of momentum imaging experiments and theory can reveal dissociation dynamics for which the axial recoil approximation breaks down and thus provides a powerful reaction microscope for DEA to polyatomics.

Ab initio calculations elucidating the complicated dissociation dynamics of dissociative electron attachment to the water molecule, when combined with COLTRIMS experimental results

We describe calculations on fragment angular distributions that complement the COLTRIMS experimental results of A. Belkacem et al. at LBNL on the subject of the coupled electronic and nuclear dynamics of dissociative electron attachment to the water molecule. Angular information from both theory and experiment may be combined to give a revealing view of the polyatomic dynamics by which the anion breaks up into H2 + O−, OH + H−, and the three body channels.

Dynamics of dissociative electron attachment in ammonia, methane and hydrogen sulphide

Kinetic energy and angular distribution of the fragment anions produced due to dissociative electron attachment resonances in simple polyatomic molecules like methane, ammonia, and hydrogen sulphide are measured using a new technique of velocity map imaging. These measurements aim at determining the electronic symmetry and dissociation dynamics of the resonance states.

Dissociative electron attachment to theH2Omolecule I. Complex-valued potential-energy surfaces for theB12,A12, andB22metastable 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 $^{2}B_{1}$, $^{2}A_{1}$, and $^{2}B_{2}$ 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 $^{2}A_{1}$ and $^{2}B_{2}$ 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 on the nuclear dynamics of dissociative electron attachment to ${\mathrm{H}}_{2}\mathrm{O}$.

Molecular dynamics of dissociative electron attachment in water

Classical trajectory calculations have been used to model dissociative electron attachment (DEA) processes in water. In previously reported experiments, DEA cross-sections show maxima at three different energies between ca. 6 and 12 eV; these have been ascribed to the formation and dissociative decay of three different resonant (anion) states of symmetry 2B1, 2A1 and 2B2 whose parent states are the Ã1 B1, B 1A1 and C 1B2 states, respectively, of neutral water. The present model calculations show that the essential features of the experimental findings can be reproduced using only two anionic potential surfaces; furthermore, most of the observed product ions follow from initial excitation to one (the lower-lying in symmetric geometries) of these. If the two surfaces are related to resonances of symmetry 2B1 and 2B2, then all of the observed features associated with resonant electron scattering from water can be rationalised.