ORCID
0000-0003-4249-7396
Keywords
Ultrafast spectroscopy, surface science, molecular dynamics, semiconducting materials
Subject Categories
Materials Chemistry | Optics | Physical Chemistry
Abstract
Understanding photoinduced reactions at solid interfaces is essential for advancing heterogeneous photocatalysis, surface photochemistry, and energy conversion technologies. This dissertation investigates the ultrafast dynamics of reactive intermediates, fragment trapping, and radical-mediated bond formation on oxide surfaces using time-of-flight mass spectrometry in conjunction with femtosecond pump-probe spectroscopy. Various experimental findings are validated through collaborations via density functional theory (DFT). By combining temporal, mass, and energy-resolved measurements, this work provides molecular-level insight into the elementary processes governing light-driven surface reactions. The photodissociation dynamics of CH3I adsorbed on TiO2(110), TiO2(100), and amorphous silicon oxide surfaces are examined as model systems for photoinduced surface chemistry. On TiO2(110), direct detection of transient intermediates reveals that photogenerated fragments can become trapped at the surface, passivating reactive sites and modifying the interfacial potential energy landscape. This fragment trapping stabilizes a previously unobserved CH3ICH3 intermediate, which alters ultrafast reaction pathways and produces coherent oscillations in transient CH3+ signals. Complementary DFT calculations identify the vibrational modes and dissociation pathways associated with this intermediate. Photocatalytic water splitting on TiO2(100) is further investigated through direct observation of elusive intermediates, including D, OD, and OOD species generated from D2O photodissociation. In the presence of CH3I, additional reaction pathways lead to methane and methanol formation through coupling between water-derived species and methyl fragments. Temperature-dependent measurements and DFT calculations clarify the mechanisms governing these photocatalytic reactions. This dissertation also demonstrates ultrafast carbon–carbon bond formation on amorphous silicon oxide surfaces following CH3I photodissociation. Time-resolved detection of C2 fragments provides direct evidence of methyl radical coupling, with product formation observed as early as ~0.5 ps after excitation. Collectively, these studies reveal how fragment trapping, energy dissipation, and radical interactions govern ultrafast surface reactivity, establishing new insights into photocatalytic and heterogeneous photochemical processes at oxide interfaces.
Completion Date
2026
Semester
Summer
Committee Chair
Dr. Mihai Vaida
Degree
Doctor of Philosophy (Ph.D.)
College
College of Sciences
Department
Department of Physics
Format
Document Type
Dissertation
Language
English
STARS Citation
Gupta, Aakash, "Deciphering ultrafast photoinduced and photocatalytic reaction dynamics on oxide surfaces: direct detection of radical intermediates, fragment trapping, and carbon–carbon, carbon–oxygen, and carbon–hydrogen bond formation pathways" (2026). Graduate Studies Theses and Dissertations 2026. 271.
https://stars.library.ucf.edu/gradstudies_etd_2026/271
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