Low-energy Electron Collision Dynamics of a few Atmospherically and Biologically Important Molecules

Paul, Anirban (2024) Low-energy Electron Collision Dynamics of a few Atmospherically and Biologically Important Molecules. PhD thesis, Indian Institute of Science Education and Research Kolkata.

Text (PhD thesis of Anirban Paul (18RS006)) 18RS006.pdf - Submitted Version Restricted to Repository staff only Download (8MB)

Abstract

The dissociation of molecules by low-energy electrons is a fundamental process in nature. It is an important process in various branches of science because it is directly related to the mechanisms of radiation-induced damage of living cells and the depletion of the ozone layer in the upper atmosphere. Radiation-induced damage of living cells due to nuclear radiation is mainly caused by the low-energy secondary electrons produced from higher-energy primary radiation. Single and double-strand breaks of DNA are also mainly caused by these low-energy secondary electrons. Dissociative electron attachment (DEA) and ion pair dissociation (IPD) are two processes in low-energy electron-molecule collisions that produce fragment anions. DEA is the dominant process in low-energy electron molecule collision processes. The typical energy range for this process is ≤ 15 eV. It is a two-step resonant process. In the first step, the incoming electron gets attached to the parent molecule, forming a temporary negative ion (TNI). In the subsequent step, this TNI dissociates to produce one anionic fragment with one or more than one neutral fragment. Unlike DEA, in the ion-pair dissociation, the target molecule does not capture the electron. Instead, the electron transfers part of its kinetic energy to the molecule and excites it, and the resulting excited molecule then dissociates into an anionic and a cationic fragment. This process starts above about 15 eV energy and continues up to a few hundred eV. The motivation behind our work on low-energy electron collision with a few atmospherically and biologically important molecules partly came from the important role played by low-energy electron collision in the upper atmosphere and various applications like radiation therapy, plasma processing, semiconductor industries, etc. The recent discovery of site-specific fragmentation and selective bond breaking in the dissociative electron attachment to biomolecules has made the low-energy electron collision more interesting to study. Consequently, using the velocity map imaging (VMI) technique, the kinetic energy and angular distributions and using the high-resolution time-of-flight mass spectrometry (TOFMS), the absolute dissociation cross sections of the fragment anions produced due to the low-energy electron collision with molecules have been measured. In accordance with this plan, this thesis is a combination of studies of DEA and IPD processes of molecules, namely - Carbon disulfide, Carbon tetra chloride, Nitrogen dioxide, Nitric oxide, Ethanol, and Ethyl acetate using the VMI and TOFMS technique, followed by their detailed dynamics.

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