Electron-impact Resonant and Quasi-resonant Charge Transfer Dissociation in Search of Beyond Dipole Transitions

Kundu, Narayan (2024) Electron-impact Resonant and Quasi-resonant Charge Transfer Dissociation in Search of Beyond Dipole Transitions. PhD thesis, Indian Institute of Science Education and Research Kolkata.

Text (PhD thesis of Narayan Kundu (18RS002)) 18RS002.pdf - Submitted Version Restricted to Repository staff only Download (21MB)

Abstract

This thesis investigates electron-impact resonant charge transfer dissociation at low beam energies (0–15 eV), focusing on dissociative electron attachment (DEA) of triatomic OCS molecules, and at intermediate beam energies (15–50 eV), with an emphasis on ion-pair dissociation (IPD) of diatomic (oxygen, carbon monoxide) and triatomic molecules (carbon dioxide, carbonyl sulfide). Utilizing advanced velocity slice anion imaging methods, the study provides fundamental insights into the dynamics of DEA and IPD. The imaging equipment, developed in-house, employs time-of-flight (TOF)- based mass spectroscopy, a 2D position-sensitive detector, three microchannel plates (MCPs), and a position-encoding delay line hexanode. A unique conical time-gated wedge slice imaging approach is introduced to overcome the limitations of traditional parallel time-gated slicing, revealing extensive molecular system analysis. The Jacobian over-parallel slicing method counters low-momentum ion exaggeration, which is beneficial when TOF information is not recorded. The conical time-gated wedge slice imaging method captures slice images, kinetic energy (KE), and angular distributions (AD) of fragments, providing a comprehensive understanding of DEA and IPD processes. Each of the reports focuses on fragments exhibiting anion-vibronic properties, revealing a non-radiative predissociation continuum through Landau- Zener quantum tunneling in avoided crossing regimes. The DEA study of OCS explores Renner-Teller and predissociation-coupled vibronic intensity borrowing, indicating a vibronic Feshbach resonance near 6.5 eV. IPD of oxygen exposes three dissociative channels for oxygen atomic anion fragmentation, exposing limitations of the dipole-Born approximation. The IPD to CO study delves into the trilobite-like S-wave quasi-resonant ion-pair binding process, akin to the Rydberg electron’s trilobite pattern. IPD to carbon dioxide unveils the butterfly ion-pair binding process, noting contributions from S and P symmetry. Non-linear dynamics in ion-pair dissociation, featuring predominant P-wave and F-wave-resonant structures, is observed in IPD to carbon dioxide. Quantum coherence is suggested in the forward and backward directions for O⁻/CO, O⁻/OCS, and S⁻/OC products during IPD. Theoretical computations are anticipated to provide deeper insights into complex dynamics. Increasing electron beam energy results in a decrease in the non-uniform nature of angular distribution, attributed to momentum transfer rotation. Moreover, each of the reports reveals at least one electronic transition that goes beyond the dipole moment, which justifies the title of this thesis. In summary, the research uncovers fundamental distinctions between free electrons’ (primary beam energy) resonant charge transfer and secondary electrons’ quasi-resonant charge transfer dissociation, highlighting their significance in heavy and ultralong Rydberg physics, plasma modeling, DNA damage, contemporary proteomics, and peptidomics.

Actions (login required)

View Item