Interstellar Metal Chemistry: Potential Energy Surface generation and Quantum Reaction Dynamics study

Roy, Arghyadeb (2025) Interstellar Metal Chemistry: Potential Energy Surface generation and Quantum Reaction Dynamics study. Masters thesis, Indian Institute of Science Education and Research Kolkata.

Text (MS Dissertation of Arghyadeb Roy (20MS146)) 20MS146_Thesis_file.pdf - Submitted Version Restricted to Repository staff only Download (36MB)

Abstract

Astrochemistry explores the intricate molecular processes shaping the Universe, with gas-phase chemistry—particularly ion-neutral reactions—playing a pivotal role in the molecular evolution of interstellar environments. While astrochemical models have traditionally emphasized non-metallic species, recent observations have revealed a richer role for metal-containing molecules, such as NaCl and KCl, challenging long-held assumptions about the chemical inertness of metals in the interstellar medium (ISM). This thesis focuses on the generation of high-accuracy potential energy surfaces (PESs) and the exploration of quantum reaction dynamics for alkaline metal hydride-involved reactions of astrochemical relevance. Specifically, detailed PESs were constructed for systems such as NaH+ + H and LiH+ + H, capturing subtle features like reaction intermediates, barriers, and complex formation. Quantum dynamical calculations were subsequently performed to investigate the reaction pathways, cross sections, and rate coefficients across a range of temperatures typical of the ISM. The reaction mechanisms unveiled in this study reveal that, although the processes are fundamentally barrierless, the reaction dynamics involve multiple competing pathways and the formation of transient complexes. The selectivity among different reactant and product states plays a significant role in shaping the reaction rates, leading to a more nuanced understanding than previously assumed. These findings emphasize the importance of accurately capturing state-to-state dynamics when modeling metal hydride chemistry in astrochemical environments. The results not only provide improved rate coefficients but also offer mechanistic insights critical for refining chemical networks used to model molecular evolution in both present-day and primordial cosmic environments.

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