Abstract
Vibrational dynamics governs the redistribution of energy in molecular and materials systems, influencing processes as diverse as light harvesting, charge transport, and chemical reactivity. Yet, in condensed-phase environments, solvent effects, lineshape broadening and spectral overlap obscure mode-specific behavior. Gas-phase experiments, where molecules are isolated under cryogenic conditions, offer a clearer window into fundamental vibrational dynamics. This dissertation presents a unified platform for probing vibrational dynamics of cold, mass-selected ions using mid infrared ultrafast laser spectroscopy paired with cryogenic ion trapping. By combining cryogenic ion vibrational spectroscopy with phase-controlled femtosecond pulse sequences, we capture both linear and nonlinear responses without interference from solvent or matrix interactions. This dissertation begins with a rhenium carbonyl complex that exhibits well-separated symmetric and asymmetric CO stretch modes. Excitation with tailored three-pulse transient absorption sequences reveals periodic oscillations in the detected signal matching the energy splitting of these modes, which is direct evidence of coherent superpositions. Extending to two-dimensional (2D) experiments, observation of cross peaks in both the metal carbonyl and in protonated caffeine demonstrate the method’s versatility. Moving to a biologically relevant peptide, protonated glutathione, we obtain time-resolved 2D IR spectra in amide I and II spectral region. While peak positions align with theoretical predictions, the time evolution of signal intensity departs from secular simulation models. We interpret this discrepancy through a coherence transfer model framework: mode superpositions redistribute oscillations over time, a subtle effect that is hard to probe in condensed-phase measurements. To streamline multidimensional data acquisition, we introduce a selective excitation protocol that is Liouville-pathway specific. By filtering excitation frequencies, we isolate chosen coherence pathways in a single measurement dimension, dramatically reducing experimental complexity while preserving sensitivity to intra- and inter-mode coherences. Application to various vibrational bands in two distinct ions confirms that oscillation frequencies between ground and excited states, and between paired excitations, can be extracted directly without a full waiting time series of 2D spectra. This dissertation delivers an integrated approach for unraveling complicated time evolution of vibrational dynamics in isolated ions. The combination of cryogenic trapping of ions and advanced pulse shaping provides a powerful toolkit for investigating fundamental dynamics free from environmental noise. These insights pave the way for future efforts to model anharmonic-coupling- and coherence-related spectral signatures within a harmonic-basis framework, providing an effective beyond-secular improvement rather than implying a literal mode-to-mode energy redistribution.
Committee Chair
Joseph Fournier
Committee Members
Joseph Fournier; Richard Loomis; Richard Mabbs; Xue-Bin Wang; Zhiling Zheng
Degree
Doctor of Philosophy (PhD)
Author's Department
Chemistry
Document Type
Dissertation
Date of Award
4-21-2026
Language
English (en)
DOI
https://doi.org/10.7936/w3v5-fm39
Recommended Citation
Ma, Zifan, "Nonlinear Ultrafast Vibrational Spectroscopy of Cryogenically Cooled Molecular Ions" (2026). Arts & Sciences Graduate Student Theses and Dissertations. 3806.
The definitive version is available at https://doi.org/10.7936/w3v5-fm39