Velocity Slice Research Articles

Probing the resonant states of Cl2 using velocity slice imaging

The negative ion resonances in molecular chlorine are probed using velocity slice imaging of the Cl− fragment produced in dissociative electron attachment (DEA). The capability of the velocity slice imaging to cover the entire 360° allows us to obtain clear evidence for the presence of the resonance in the 2.5 eV DEA peak along with the presence of The resonance is expected to be the contributor only to the 0 eV DEA peak. Its presence in the 2.5 eV DEA peak calls for a relook at the theoretical calculations which have not identified any resonance in the 2.5 eV peak. We also identify the presence of the and resonances in the 5.6 eV peak. The momentum images indicate no signature of a resonant contribution in the dipolar dissociation region up to 80 eV.

Dissociative electron attachment to chlorine dioxide probed by velocity slice im-aging

SynopsisWe report the study of dissociative electron attachment (DEA) to chlorine dioxide (OClO) in the energy range of 1 to 10 eV using velocity slice imaging technique. DEA to OClO shows Cl−, O−, O2−, and OCl− as fragment channels at various electron energies. Based on the momentum images of these ions we unravel the molecular dynamics leading to DEA.

Dissociative electron attachment dynamics of ozone using velocity slice imaging

SynopsisWe report the study of dissociative electron attachment to ozone (O3) in the energy range of 1 to 10 eV using velocity slice imaging technique. Based on the momentum images that we obtained for O− and O2− channels at various electron energies we unravel the molecular dynamics leading to DEA.

Dissociative electron attachment to molecular chlorine

SynopsisWe report the study of dissociative electron attachment to molecular chlorine in the energy range of 1 to 20 eV using velocity slice imaging technique. Based on the angular distributions at various electron energies, we identify the partial waves involved in the resonance formation that lead to DEA.

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.

Fragmentation dynamics in dissociative electron attachment to CO probed by velocity slice imaging.

Complete dissociation dynamics in electron attachment to carbon monoxide (CO) have been studied using the newly developed velocity slice imaging (VSI) technique. Both kinetic energy and angular distributions of O(-) ions formed by dissociative electron attachment (DEA) to CO molecules have been measured for 9, 9.5, 10, 10.5, 11, and 11.5 eV incident electron energies around the resonance. Detailed observations conclusively show that two separate DEA reactions lead to the formation of O(-) ions in the ground (2)P state along with the neutral C atoms in the ground (3)P state and the first excited (1)D state, respectively. Within the axial recoil approximation and involving four partial waves, our angular distribution results clearly indicate that the two reactions leading to O(-) formation proceed through the specific resonant state(s). For the first process, more than one intermediate state is involved. On the other hand, for the second process, only one state is involved. The observed forward-backward asymmetry is explained in terms of the interference between the different partial waves that are involved in the processes.

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.

State Selectivity and Dynamics in Dissociative Electron Attachment to CF3I Revealed through Velocity Slice Imaging

AbstractIn light of its substantially more environmentally friendly nature, CF3I is currently being considered as a replacement for the highly potent global‐warming gas CF4, which is used extensively in plasma processing. In this context, we have studied the electron‐driven dissociation of CF3I to form CF3− and I, and we compare this process to the corresponding photolysis channel. By using the velocity slice imaging (VSI) technique we can visualize the complete dynamics of this process and show that electron‐driven dissociation proceeds from the same initial parent state as the corresponding photolysis process. However, in contrast to photolysis, which leads nearly exclusively to the 2P1/2 excited state of iodine, electron‐induced dissociation leads predominantly to the 2P3/2 ground state. We believe that the changed spin state of the negative ion allows an adiabatic dissociation through a conical intersection, whereas this path is efficiently repressed by a required spin flip in the photolysis process.

State Selectivity and Dynamics in Dissociative Electron Attachment to CF3I Revealed through Velocity Slice Imaging

In light of its substantially more environmentally friendly nature, CF3I is currently being considered as a replacement for the highly potent global-warming gas CF4, which is used extensively in plasma processing. In this context, we have studied the electron-driven dissociation of CF3I to form CF3(-) and I, and we compare this process to the corresponding photolysis channel. By using the velocity slice imaging (VSI) technique we can visualize the complete dynamics of this process and show that electron-driven dissociation proceeds from the same initial parent state as the corresponding photolysis process. However, in contrast to photolysis, which leads nearly exclusively to the (2)P(1/2) excited state of iodine, electron-induced dissociation leads predominantly to the (2)P(3/2) ground state. We believe that the changed spin state of the negative ion allows an adiabatic dissociation through a conical intersection, whereas this path is efficiently repressed by a required spin flip in the photolysis process.

Velocity slice imaging study on dissociative electron attachment to CF4

A Velocity Slice Imaging (VSI) study on Dissociative Electron Attachment (DEA) to carbon tetrafluoride, CF4, is presented. Two fragments are observed; F− produced from two, partly overlapping, resonances and CF3 − deriving from a single resonance. The angular distributions of these anionic fragments and their kinetic energy distributions are reported and are then discussed in context of the influence of the Jahn-Teller effect on the symmetry of the resonant states involved.

Dissociative electron attachment and dipolar dissociation in ethylene

We present a detailed experimental investigation of anion production in electron collisions with ethylene, C2H4. The investigated energy range is between 0 and 90eV where anions are formed by two processes, in the low energy regime by dissociative electron attachment (DEA) and at higher energy by dipolar dissociation (DD). These electron induced processes are studied in two different experimental apparatus using two different mass spectrometry techniques. One is a time of flight spectrometer operating with velocity slice imaging technique and the other is a two sector field mass spectrometer. The former allows efficient collection of ions compared to standard mass spectrometers, while the latter provides high mass resolution. Eight fragment anions formed via DEA in the electron energy range between 5 and 17eV have been detected; two fragments have not reported as DEA products in any previous studies. DD in C2H4 leads to the formation of the same anions as found in the case of DEA. Quantum chemical calculations have been carried out to determine the thermochemical thresholds of anion formation.

Dissociative electron attachment to N2O using velocity slice imaging

The structure and dynamics of the negative ion resonances leading to dissociative electron attachment in N2O are studied using the velocity slice imaging technique. Distinct momentum distributions are observed in the O(-) channel for the dominant resonances below 4 eV which are considerably different than those reported so far. Also the relatively weak but distinct resonances at 8.1 eV and 13.2 eV are studied for their dynamics for the first time. For each of these resonances two different channels of dissociation are observed with differing angular distributions.

CHARACTERIZING THE TURBULENT PROPERTIES OF THE STARLESS MOLECULAR CLOUD MBM 16

We investigate turbulent properties of the non-star-forming, translucent molecular cloud, MBM16 by applying the statistical technique of a two-dimensional spatial power spectrum (SPS) on the neutral hydrogen (HI) observations obtained by the Galactic Arecibo L-Band Feed Array HI (GALFA-HI) survey. The SPS, calculated over the range of spatial scales from 0.1 to 17 pc, is well represented with a single power-law function, with a slope ranging from -3.3 to -3.7 and being consistent over the velocity range of MBM16 for a fixed velocity channel thickness. However, the slope varies significantly with the velocity slice thickness, suggesting that both velocity and density contribute to HI intensity fluctuations. By using this variation we estimate the slope of 3D density fluctuations in MBM16 to be -3.7\pm0.2. This is significantly steeper than what has been found for HI in the Milky Way plane, the Small Magellanic Cloud, or the Magellanic Bridge, suggesting that interstellar turbulence in MBM16 is driven on scales >17 pc and that the lack of stellar feedback could be responsible for the steep power spectrum.

Quantum Superposition of Target and Product States in Reactive Electron Scattering fromCF4Revealed through Velocity Slice Imaging

Exploiting the technique of velocity slice imaging, we have performed a detailed study of reactive electron scattering with CF4. We have measured the electron impact energy dependence of both the angular and kinetic energy distributions of the channels yielding F- and CF3(-) anions. These data provide an unprecedented insight into the quantum superposition of the target state and product channels, respectively, of Td and C3v symmetry, and shed new light on the dissociation dynamics.

Two- and Three-Body Dissociation Dynamics of Temporary Negative Ion NF3–

Dissociation dynamics of temporary negative ion NF3(-) formed in the low-energy (0.5 to 4.5 eV) electron attachment is investigated by the anion velocity slice imaging spectroscopy. The kinetic and angular distributions of the F(-) fragment indicate that this fragment is produced via two distinctly different dissociation channels, namely, two-body and three-body fragmentations, at the higher electron attachment energies. The anisotropic distributions of the fast F(-) ions are interpreted as the two-body dissociations relevant to the (2)E resonant state of NF3(-), whereas the slow F(-) can be produced via various three-body dissociations with the products of NF(X (3)Σ(-)) + F + F(-), NF(b (1)Σ(+)) + F + F(-), or N + F2 + F(-), depending on the electron attachment energy.

Dissociative electron attachment to acetaldehyde, CH3CHO. A laboratory study using the velocity map imaging technique

A detailed experimental investigation of the dissociative electron attachment (DEA) process to acetaldehyde, CH(3)CHO is presented. To investigate this process we use a time of flight spectrometer coupled with the velocity slice imaging technique. DEA in CH(3)CHO is found to lead to the formation of CH(3)(-), O(-), OH(-), C(2)H(-), C(2)HO(-) and CH(3)CO(-) anionic products produced through scattering resonances in the electron energy range of 6 to 13 eV. Of these product ions only O(-) is formed with any measurable kinetic energy distribution indicating a two-body dissociation process. CH(3)CO(-), although formed with very low kinetic energy, shows anisotropy in the velocity slice image, indicating ejection of the H atom in the 180° direction with respect to the electron beam. The low kinetic energy distributions and absence of any anisotropy in the angular distributions of the other product ions indicate that they are formed through multiple fragmentation of the transient molecular negative ion. The angular distribution of O(-) is analysed in terms of the various partial waves.

Dissociative electron attachment to CF4 probed by Velocity Slice Imaging

We present the experimental setup for Velocity Slice Imaging and the results of measurements on F− and CF−3 from CF4.

Velocity Slice Imaging of X− fragments from CF3X (X=Cl, Br and I) upon Dissociative Electron Attachment

The Dissociative Electron Attachment resonances of CF3X (X=Cl, Br and I) yielding X− at low energy are probed by Velocity Slice Imaging

Dissociative electron attachment resonances in ammonia: A velocity slice imaging based study

Negative ion resonance states of ammonia are accessed upon capture of electrons with energy 5.5 eV and 10.5 eV, respectively. These resonance states dissociate to produce H(-) and NH(2)(-) fragment anions via different fragmentation channels. Using the velocity slice imaging technique, we measured the angular and kinetic energy distribution of the fragment H(-) and NH(2)(-) anions with full 0-2π angular coverage across the two resonances. The scattered H(-) ions at both resonances show variation in their angular distribution as a function of the kinetic energy indicating geometric rearrangement of NH(3)(-*) ion due to internal excitations and differ from the equilibrium geometry of the neutral molecule. The second resonance at 10.5 eV shows strong forward-backward asymmetry in the scattering of H(-) and NH(2)(-) fragment ions. Based on the angular distributions of the H(-) ions, the symmetry of the resonances at 5.5 eV and 10 .5 eV are determined to be A(1) and E, respectively, within C(3v) geometry.

Dynamics of the dissociative electron attachment in H2O and D2O: The A1 resonance and axial recoil approximation#

The dynamics of the formation and decay of negative ion resonance of A1 symmetry at 8.5 eV electron energy in the dissociative electron attachment (DEA) process in H2O and D2O are investigated using the velocity slice imaging technique. While the highest energy hydride ions formed by DEA show angular distributions characteristic to the A1 symmetry, those formed with low-kinetic energy show considerably different angular distributions indicating changes in the orientation of the dissociating bond due to bending mode vibrations. Our observations are quite different from the recently reported measurements, but consistent with the fully quantum calculations. Dynamics of the 2A1 negative ion resonance in water is probed using velocity slice imaging of H– from H2O and D– from D2O. While the momentum distributions of the highest energy ions agree with quantum calculations, those of low energy ions indicate the role of bending mode excitations before dissociation.