Ultrafast dynamics of small quantum systems studied using electron-ion coincidence spectroscopy
(2023)- Abstract
- Studying how small quantum systems, like molecules and clusters, interact with X-rays is crucial to understanding the ultrafast processes that occur in nature on incredibly short timescales, ranging from femtoseconds to picoseconds. X-rays excite small quantum systems to unstable core hole states, leading to a cascade of phenomena, including Auger decay, nuclear rearrangement, and dissociation. The dissociation of molecules is influenced by the initial site of X-ray excitation, as well as the properties of the Auger populated states, such as charge localization and internal energy. In clusters, the dissociation process depends on intermolecular interactions, cluster size, and geometry. The interplay between electronic and nuclear dynamics... (More)
- Studying how small quantum systems, like molecules and clusters, interact with X-rays is crucial to understanding the ultrafast processes that occur in nature on incredibly short timescales, ranging from femtoseconds to picoseconds. X-rays excite small quantum systems to unstable core hole states, leading to a cascade of phenomena, including Auger decay, nuclear rearrangement, and dissociation. The dissociation of molecules is influenced by the initial site of X-ray excitation, as well as the properties of the Auger populated states, such as charge localization and internal energy. In clusters, the dissociation process depends on intermolecular interactions, cluster size, and geometry. The interplay between electronic and nuclear dynamics in core-excited/ionized molecules and clusters is a critical factor that needs to be assessed.
This thesis investigates X-ray-induced fragmentation of molecular adamantane and CO2 clusters using synchrotron radiation. The kinematics of molecular and cluster fragmentation is measured using advanced techniques, such as 3D momentum imaging of the ion fragments and multiparticle coincidence spectroscopy. Site-selective fragmentation of the carbon cage of the adamantane molecule is studied using Auger-electron Photoion coincidence spectroscopy, revealing the influence of the core-hole site on the Auger decay and dissociation process. Statistical data analysis treatment is developed and implemented to remove background contamination in the coincidence data using experimental random coincidences. The results highlight that the fragmentation of adamantane cation and dication is a complex dynamical process with competing relaxation pathways involving cage opening, hydrogen migration, and carbon-carbon bond breaking. Additionally, the thesis investigates the photoreactions of core-ionized CO2 clusters, reporting a significantly increased production of O2+ compared to isolated CO2 molecules. Through quantum chemistry calculations and multi-coincidence 3D momentum imaging, the study determined that the enhanced production of O2+ is due to a size-dependent structural transition of the clusters. The study also proposes two relevant photoreactions involving intermolecular interactions.
This thesis highlights the complexity of core-hole dynamics in molecular and cluster chemistry and emphasizes the need for meticulous experimental and theoretical investigations of the underlying mechanisms. It also discusses the relevance of the results in the context of X-ray-induced astrochemistry. Indeed, the experiments presented are conducted in vacuum chambers in a controlled environment and can crudely replicate the conditions found in astrophysical environments. From the adamantane study, we conclude that X-ray absorption emphatically results in dissociation into smaller hydrocarbons and low photostability can play a part in the absence of diamondoids in the interstellar medium. From the CO2 clusters study, we found an enhancement in the O2+ yield, which can significantly influence the ion balance in CO2-rich atmospheres like Mars. (Less)
Please use this url to cite or link to this publication:
https://lup.lub.lu.se/record/4b983d32-7fe7-424f-bf37-57dca457d346
- author
- Ganguly, Smita LU
- supervisor
- opponent
-
- Professor Jahnke, Till, Frankfurt University
- organization
- publishing date
- 2023-05-22
- type
- Thesis
- publication status
- published
- subject
- keywords
- coincidence spectroscopy, photodissociation dynamics, fragmentation reaction, MOLECULAR-BEAM, Cluster fission, Astrochemistry, Carbon dioxide (CO2);, Adamantane
- pages
- 207 pages
- publisher
- Lund
- defense location
- Rydberg Lecture hall. Join via Zoom: https://lu-se.zoom.us/j/64141112402?pwd=cVJIWUxHbXorOGdaclMzaGhJSHdrdz09 passcode: 107150
- defense date
- 2023-06-16 13:15:00
- ISBN
- 978-91-8039-726-1
- 978-91-8039-725-4
- language
- English
- LU publication?
- yes
- id
- 4b983d32-7fe7-424f-bf37-57dca457d346
- date added to LUP
- 2023-05-03 14:28:47
- date last changed
- 2023-05-22 12:15:59
@phdthesis{4b983d32-7fe7-424f-bf37-57dca457d346,
abstract = {{Studying how small quantum systems, like molecules and clusters, interact with X-rays is crucial to understanding the ultrafast processes that occur in nature on incredibly short timescales, ranging from femtoseconds to picoseconds. X-rays excite small quantum systems to unstable core hole states, leading to a cascade of phenomena, including Auger decay, nuclear rearrangement, and dissociation. The dissociation of molecules is influenced by the initial site of X-ray excitation, as well as the properties of the Auger populated states, such as charge localization and internal energy. In clusters, the dissociation process depends on intermolecular interactions, cluster size, and geometry. The interplay between electronic and nuclear dynamics in core-excited/ionized molecules and clusters is a critical factor that needs to be assessed. <br/>This thesis investigates X-ray-induced fragmentation of molecular adamantane and CO<sub>2</sub> clusters using synchrotron radiation. The kinematics of molecular and cluster fragmentation is measured using advanced techniques, such as 3D momentum imaging of the ion fragments and multiparticle coincidence spectroscopy. Site-selective fragmentation of the carbon cage of the adamantane molecule is studied using Auger-electron Photoion coincidence spectroscopy, revealing the influence of the core-hole site on the Auger decay and dissociation process. Statistical data analysis treatment is developed and implemented to remove background contamination in the coincidence data using experimental random coincidences. The results highlight that the fragmentation of adamantane cation and dication is a complex dynamical process with competing relaxation pathways involving cage opening, hydrogen migration, and carbon-carbon bond breaking. Additionally, the thesis investigates the photoreactions of core-ionized CO<sub>2</sub> clusters, reporting a significantly increased production of O<sub>2</sub><sup>+</sup> compared to isolated CO<sub>2</sub> molecules. Through quantum chemistry calculations and multi-coincidence 3D momentum imaging, the study determined that the enhanced production of O<sub>2</sub><sup>+</sup> is due to a size-dependent structural transition of the clusters. The study also proposes two relevant photoreactions involving intermolecular interactions. <br/>This thesis highlights the complexity of core-hole dynamics in molecular and cluster chemistry and emphasizes the need for meticulous experimental and theoretical investigations of the underlying mechanisms. It also discusses the relevance of the results in the context of X-ray-induced astrochemistry. Indeed, the experiments presented are conducted in vacuum chambers in a controlled environment and can crudely replicate the conditions found in astrophysical environments. From the adamantane study, we conclude that X-ray absorption emphatically results in dissociation into smaller hydrocarbons and low photostability can play a part in the absence of diamondoids in the interstellar medium. From the CO<sub>2</sub> clusters study, we found an enhancement in the O<sub>2</sub><sup>+</sup> yield, which can significantly influence the ion balance in CO<sub>2</sub>-rich atmospheres like Mars.}},
author = {{Ganguly, Smita}},
isbn = {{978-91-8039-726-1}},
keywords = {{coincidence spectroscopy; photodissociation dynamics; fragmentation reaction; MOLECULAR-BEAM; Cluster fission; Astrochemistry; Carbon dioxide (CO2);; Adamantane}},
language = {{eng}},
month = {{05}},
publisher = {{Lund}},
school = {{Lund University}},
title = {{Ultrafast dynamics of small quantum systems studied using electron-ion coincidence spectroscopy}},
url = {{https://lup.lub.lu.se/search/files/145740467/Thesis_Smita_Ganguly_without_papers.pdf}},
year = {{2023}},
}