Quantum and Classical Dynamics for Certain Elementary Gas-Phase Reactions

Dey, Diptesh (2017) Quantum and Classical Dynamics for Certain Elementary Gas-Phase Reactions. PhD thesis, Indian Institute of Science Education and Research Kolkata.

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Abstract

Chemical reactions, the transformation of matter from reactants to products are of fundamental importance in all aspects of life as it governs the function and evolution of a chemical system. They consist of a sequence of individual sub-steps, the so-called elementary reactions which directly express the basic chemical events, that is, breaking and making of chemical bonds. The history of change involved in such elementary chemical process like how reagent molecules approach, collide, exchange energy, and fonally separate into products can be quantitatively understood through the study of molecular reaction dynamics. It provides a microscopic description of chemical reactions on the fundamental scale of atoms and molecules. The field of molecular reaction dynamics encompasses a wide range of research areas and therefore it has become an integral part of modern chemistry. Among the many elementary chemical reactions studied, there has been signifocant progress in the dynamical studies of gas-phase reactions and our understanding has been deepened. Although the development in the field of molecular reaction dynamics till now is noteworthy, yet there are many aspects where we conceptually lack understanding of the basic principles and particular details that govern the chemical process, resulting in many unanswered questions. The objective of this thesis is to address some of these fundamental issues and to obtain a detailed understanding of the elementary gas-phase reactions which have realworld applications in atom-molecule reactive scattering, laser-induced control of chemical reactions, laser-driven electron-nuclei correlated motion, and ultimately the most vital, laser-induced ultrafast electron dynamics in attosecond time scales. For implementation purpose, either time-dependent quantum wave packet dynamics or classical dynamics has been used as numerical tools based upon their convenience and also our results have been compared with available experimental studies. The thesis is outlined as follows: Chapter 1 gives a general introduction in the field of molecular reaction dynamics along with its present challenges. Chapter 2 presents a brief overview of various theoretical techniques used in this study. Chapter 3 reports a quantum dynamical study on the effect of orientation and rotation of the hydrogen molecule on the atmospherically important reaction: S(¹D) + H₂(X¹∑⁺g)(v = 0; j =0 - 3) → SH(X²π) + H(¹S). Chapter 4 reports a quantum mechanical study on the influence of different initial vibrational states governing the dissociation dynamics of HOD²⁺. Chapter 5 reports the laser-induced coupled electron-nuclear dynamical study of H⁺₂ within time-dependent Born-Oppenheimer approximation. Chapter 6 reports a classical dynamical study on the effect of carrier-envelope-phase of intense, few-cycle laser pulses influencing the ionization dynamics of carbon atom. Finally, Chapter 7 summarizes the important results of this thesis and presents possible future work and outlook.

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