Coupled Electron-Nuclear Dynamics of H⁺₂ and H₂ Under the Influence of Strong Laser Pulses

Pandey, Gaurav (2022) Coupled Electron-Nuclear Dynamics of H⁺₂ and H₂ Under the Influence of Strong Laser Pulses. PhD thesis, Indian Institute of Science Education and Research Kolkata.

Text (PhD thesis of Gaurav Pandey (17RS036)) 17RS036.pdf - Submitted Version Restricted to Repository staff only Download (5MB)

Abstract

Understanding the fundamental nature of chemical reactions and controlling them in real-time is one of the primary interests of chemical physics and physical chemistry. On the microscopic level, chemical reactions are governed by electronic and nuclear dynamics with timescale of attosecond (10⁻¹⁸ seconds) and femtosecond (10⁻¹⁵ seconds), respectively. Laser pulses can achieve this ultrafast timescale with very high precision. With the advent of current laser technology, it is now possible to generate highly intense ultrashort laser pulses which can be used to image and control the electronic and nuclear dynamics in real-time. When a laser pulse with low intensity interacts with a molecular system, it does not distort the potential energy surface (PES) or its electronic structure; thereby, the difference in the timescale of electronic and nuclear motion persists. This becomes the basis of the Born-Oppenheimer approximation. However, when a strong laser pulse interacts with a molecule, it greatly distorts the PES, which makes the timescales of electronic and nuclear motion comparable. This leads to the breakdown of Born-Oppenheimer approximation and requires the coupled treatment of both electronic and nuclear motions. This coupled electron-nuclear dynamics in molecules is the basis of the work presented in this thesis. The thesis aims to answer the fundamental questions of the laser-induced coupled electron-nuclear dynamics of molecules. The study is mainly focused on the one electron and two electron molecular systems, such as, HD⁺,H⁺₂ , and H₂ molecule. Various strong field phenomena, including dissociation and ionization are induced by exposing molecules by intense, ultrashort linearly and elliptically polarized laser pulses. Both quasi-classical and quantum dynamical methods have been used to simulate the ultrafast processes in these molecules and the results have been compared with recent experimental studies. The thesis is outlined as follows: Chapter 1 gives a general introduction to the field of ultrafast dynamics with its present challenges. Chapter 2 gives an overview of the theoretical methods used to perform the calculations. Chapter 3 reports the quasi-classical dynamics of the HD⁺ molecular ion in intense linearly polarized pulse. Chapter 4 presents a quasi-classical dynamics of the H2 molecule focusing on the double ionization and dissociation processes . Chapter 5 reports the quasi-classical dynamics of H₂ molecule investigating the role of molecular orientation and the CEP of the elliptically polarized laser pulse. Chapter 6 presents a comparison of quasi-classical and quantum dynamics calculations of coupled electron-nuclear dynamics of H⁺₂ in a linearly polarized intense laser pulse. Finally, Chapter 7 summarizes the important results of this thesis and presents possible future work.

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