N. Bhargava Ram

Resonances in dissociative electron attachment to water

Dissociative electron attachment to H 2 O and D 2 O is studied using the recently developed ion momentum imaging spectrometer. We obtain the kinetic energy distribution and the angular distribution in the entire 2π range in the plane of the electron beam for H - and O - ions at the three well-known resonances. While the results at the first resonance at 6.5 eV are in excellent agreement with existing experimental and theoretical results, the angular distributions of the ions at the second (8.5 eV) and third resonance (11.8 eV) are considerably different from the available data. The angular distribution at 11.8 eV shows a very unique distribution of the H - ions in the backward hemisphere, while that of the O - ions is in the forward hemisphere. Based on our results, we reassign the symmetry of the resonance seen at 8.5 eV as a B 1 state instead of A 1 as believed till now. The kinetic energy distribution of H - at the third resonance clearly indicate three dissociation channels leading to the formation of the OH radical in the ground and first electronically excited state as well as a complete three-body breakup.

Probing site selective fragmentation of molecules containing hydroxyl group using Velocity Slice Imaging

Site selective fragmentation is observed at the hydrogen site in small organic molecules like simple carboxylic acids and alcohols in the dissociative attachment (DA) process. We have investigated this site selectivity in the acetic acid and methanol molecules by measuring the kinetic energy and angular distribution of the hydride ions using Velocity Slice Imaging (VSI) technique. The results are explained in terms of the formation of valance excited Feshbach resonances. The kinetic energy and angular distribution measurements also reveal the dynamics associated with the process.

Velocity Map Imaging of H- Ions from Dissociative Electron Attachment to H2O

The velocity map imaging (VMI) technique developed recently for dissociative electron attachment (DEA) experiments is improvised further to study the formation of H− ions. The experiment is used to study DEA to water molecules at the 6.5 eV and 8.5 eV resonances. The kinetic energy and angular distribution of the H− ions arising from this resonance are compared with those in the existing experimental and theoretical data.

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.