Dissociative electron attachment to CF2Cl2

Using a recently constructed high resolution crossed electron/molecular beam apparatus consisting of a hemispherical electron monochromator and a quadrupole mass spectrometer we have measured the relative production cross sections for CI^– and F^– via electron attachment to CF₂Cl₂. The relative Cl^– cross section is placed on an absolute scale by reference to an absolute rate coefficient using a calibration method involving integration of the measured anion signal. The most efficient Cl^– production process is at about zero energy and its magnitude is resolution limited. The present high resolution value of 6 × 10^–16 cm² compares well with an earlier value reported by Chen and Chantry. A second peak is detected at around 0.8 eV in accordance with some of the earlier beam and swarm measurements. The observed production of F^– has an appearance energy of 1.9 eV and the energy of maximum cross section is 3.36 eV, the latter value comparing well with several previous studies.     

Dissociative electron attachment to DNA

Electron-stimulated desorption of anions from thin films of linear and supercoiled DNA is investigated in the range 3-20 eV. Resonant structures are observed with maxima at 9.4+/-0.3, 9.2+/-0.3, and 9.2+/-0.3 eV, respectively, in the yield dependence of H-, O-, and OH- on the incident electron energy. Their formation is attributed to dissociative electron attachment.     

Theory of electron attachment to CO2 clusters

A theory of electron collisions with van der Waals clusters is developed which is capable of describing the vibrational Feshbach resonances (VFRs) recently observed in electron attachment to CO2 clusters. The calculations also predict vibrational excitation (VE) of one molecular unit in a cluster environment and demonstrate a strong influence of the VFRs on the VE cross sections.     

Dissociative attachment of an electron to a molecule: kinetic theory

Test particles interact with a medium by means of a bimolecular reversible chemical reaction. Two species are assumed to be much more numerous so that they are distributed according to fixed distributions: Maxwellians and Dirac's deltas. Equilibrium and its stability are investigated in the first case. For the second case, a system is constructed, in view of an approximate solution.     

Dissociative electron attachment to CF<Subscript>3</Subscript>Cl

We have performed an extensive experimental study of dissociative electron attachment (DEA) to CF₃Cl. Exploiting the recently developed velocity slice imaging technique, we have recorded both angular distributions and kinetic energy release of the product fragment anions of Cl⁻ and F⁻. The DEA process is dominated by the formation of resonances the symmetry of which have been explored and compared with earlier measurements. A new resonance has been identified in the F⁻ formation channel.     

Dissociative attachment of electrons to excited molecules

The development and the first results from an experiment to carry out dissociative attachment to excited molecules are discussed. A brief summary of the relevance and status of such measurements are given. Apart from measuring the absolute cross sections from excited and state selected SO₂ molecule, we have been able to characterize the negative ion resonances using the excited state dissociative attachment. In addition, the state specificity of the electron attachment process has been used to derive information on the excited neutral state itself which has not been possible using optical spectroscopy. The applicability of this technique to other species are also discussed.     

Dissociative ionization cross sections of CO2 at electron impact energy of 5 keV

The dissociative ionization of CO2 induced by 5 keV electrons in two-body and three-body dissociative channels of CO2＋2 and CO3＋2 is identified by the ion-ion coincidence- method using a momentum imaging spectrometer. The partial ionization cross sections （PICSs） of different ionic fragments are measured and the results generally agree with the calculations made by a semi-empirical approach. Furthermore, the PICSs of the dissociative channels are also obtained by carefully considering the detection efficiency of the micro-channel plates and the total transmission efficiency of the time of flight system.     

Dissociative electron attachment to the explosive detection taggant 2,3-dimethyl-2,3-dinitrobutane (DMNB)

A detailed study on dissociative electron attachment (DEA) to 2,3-dimethyl-2,3-dinitrobutane (DMNB) in the gas phase is presented. Ion yields as a function of the incident electron energy from about 0 to 14 eV have been measured for the most dominant fragments including anions such as NO₂ ⁻, [M-NO₂]⁻ or N₂O₄ ⁻. To help identifying which anion and neutral fragments are formed upon electron attachment we calculated the thermodynamic thresholds using the G4(MP2) method.     

Dissociative electron attachment to phosphoric acid esters: the direct mechanism for single strand breaks in DNA

We use dibutyl phosphate to simulate the behavior of the phosphate group in DNA towards the attack of low energy electrons. We find that the compound undergoes effective dissociative electron attachment within a low energy resonant feature at 1 eV and a further resonance peaking at 8 eV. The dissociative electron attachment (DEA) reactions are associated with the direct cleavage of the C-O and the P-O bond but also the excision of the PO-, PO3-, H2PO3- units. For the phosphate group coupled in the DNA network these reactions represent single strand breaks. We hence propose that the most direct mechanism of single strand breaks occurring in DNA at subexcitation energies (< 4 eV) is due to DEA directly to the phosphate group.     

利用基于荧光屏探测器的质谱方法研究邻位二氯苯的电子贴附解离 (cited: 1)

在自制的负离子速度成像装置上发展了负离子质谱技术．测量获得了电子贴附解离邻位二氯苯产物Cl^-的0.2～8 eV效率谱,并且在两个峰位1.2和6.0 eV测量了其切片速度影像．     

Dissociative attachment of low-energy electrons to vibrationally excited hydrogen molecules

Dissociative electron attachment to hot hydrogen molecules is studied in the framework of nonlocal resonance model. The method based on the use of the Bateman approximation, well known in nuclear physics, is adapted for solving the Lippmann-Schwinger integral equation of the nonlocal resonance model and applied to the calculation of cross sections of inelastic resonant electron-molecule collisions. The proposed method is compared with the Schwinger-Lanczos algorithm used extensively for the treatment of these processes. It is shown that the Bateman approximation is very useful and efficient for treating the non-separable nonlocal potentials appearing in the integral kernels of the nonlocal resonance models. The calculated cross sections for the dissociative attachment of electrons to vibrationally excited hydrogen molecules are of importance for astrophysics. This paper is dedicated to Prof. J. Bičák on the occasion of his 60th birthday.     

Threshold photoelectron spectrum of CO by electron attachment (TPSA)

The threshold photoelectron spectrum of CO is reported in the photon energy range from 14.0 eV (photoionization threshold) to 21 eV. The technique used is threshold photoelectron spectroscopy by electron attachment (TPSA). Vibrational levels of the X²Σ⁺ state are observed up to high quantum numbers (ν′? 12) and their population is found to be enhanced by resonant autoionization. Levels in the A²Π and B²Σ⁺ states are also observed. Here, the measured vibrational populations more closely follow Franck—Condon intensities, so that for these states direct photoionization is more important. Qualitative molecular-orbital arguments are given to make plausible the enhancements observed in CO⁺ and in previous measurements on N₂⁺.     

Dissociative attachment of low-energy electrons to vibrationally excited molecules using a photoelectron source

The process of dissociative attachment (DA) of low-energy electrons ) to vibrationally excited sodium dimer molecules is studied with high electron energy resolution () in a supersonic molecular beam. A novel photoelectron source, based on two-step photoionization of the sodium atoms in the beam, may deliver a current of up to 1 nA and has been used with a current of typically 0.2 nA in this experiment. The energy dependence of the rate of sodium anion formation is determined by ion detection based on a time-of-flight analysis. The molecules are selectively excited to levels using the technique of coherent population transfer by delayed pulses (STIRAP). The comparison of the experimental data with recent resonance model calculations based on improved potential curves reveals generally good agreement for levels v ”>12. For some distinct differences between theoretical and experimental results persist. Received: 21 November 1998 / Received in final form: 7 April 1999     

Low energy electron attachment to formic acid

Using a high resolution electron energy monochromator low energy electron attachment to formic acid is studied for the first time by means of mass spectrometric detection of the product anions. The largest dissociative electron attachment (DA) cross-section produces HCOO ^-+H with weaker channels for OH^- and O^- becoming apparent at higher incident energies. Received 23 January 2002 and Received in final form 9 February 2002 Published online 13 September 2002     

Observation of p-wave threshold behavior in electron attachment to F2 molecules

Using the high resolution laser photoelectron attachment method, we demonstrate that the cross section for F- formation due to electron capture by F2(X{1}Sigma{g}{+}) molecules at very low energies exhibits p-wave threshold behavior. This finding confirms the theoretical expectation that low-energy attachment to F2 proceeds through the F2{-}(2Sigma{u}{+}) p-wave shape resonance in contrast with previous experimental claims for s-wave threshold behavior.     

Nondissociative electron attachment to molecules and clusters

We present results of effective range theory calculations of nondissociative electron attachment to SF₆ molecules and CO₂ clusters. The first process is strongly influenced by the SF^-₆ virtual state, and the second by vibrational Feshbach resonances associated with electron capture by the long-range polarization field of the cluster with simultaneous vibrational excitation of one molecular unit. We also study how both processes depend on the initial vibrational excitation of the target. We obtain a noticeable dependence of the attachment cross-section on the symmetric stretch vibration of SF₆, although it does not lead to a significant temperature dependence at low electron energies.     

Dynamics of low-energy electron attachment to formic acid

Low-energy electrons (<2 eV) can fragment gas phase formic acid (HCOOH) molecules through resonant dissociative attachment processes. Recent experiments have shown that the principal reaction products of such collisions are formate ions (HCOO-) and hydrogen atoms. Using first-principles electron scattering calculations, we have identified the responsible negative ion state as a transient pi* anion. Symmetry considerations dictate that the associated dissociation dynamics are intrinsically polyatomic: a second anion surface, connected to the first by a conical intersection, is involved in the dynamics and the transient anion must necessarily deform to nonplanar geometries before it can dissociate to the observed stable products.