Amy Mullin

Research in the Mullin group asks fundamental questions about the role of energy in chemistry. We use time-resolved laser spectroscopy to investigate how energy is used in chemical processes and collisions at the molecular level. Our research combines pulsed laser spectroscopy and extremely high-resolution optical probes to prepare molecules in excited states and interrogate how that energy is dissipated through reactive and inelastic collisions. Areas of interest include:

Transient spectroscopy of collisions
Chemical reactions are intimately linked to molecular collisions. Collisions can impart energy to help reactants overcome energy barriers. Collisions can also deactivate a reactive molecule by removing the energy required for reactions. These processes are particularly important for molecules in high temperature environments (up to 4000 K) such as those of combustion, plasmas and the atmosphere. Our group uses time-resolved high-resolution optical absorption to study the relationship between molecular structure and collision dynamics in molecules that have been prepared in very high energy states using pulsed laser excitation. These studies measure complete energy profiles for the vibrational, rotational and translational degrees of freedom that result from collisions and yield important information about mechanisms and rates of energy loss pathways through collisions. We complement our experimental studies using classical trajectory calculations to simulate collisional energy transfer and identify the means by which intermolecular potential energy surfaces impact collisional energy flow.

Driving chemical reactions with vibrational energy
High-resolution optical probing is a powerful tool for investigating molecular processes on a microscopic level. We are using this approach to investigate at a quantum-state resolved level how chemical reactions are affected by large amounts of energy in the vibrational degrees of the reacting molecules. These studies provide detailed information about the types of molecular motion enhance (and turn off) chemical reactivity. One goal of this project is to design reactions that can be turned on and off by external control.

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Spinning molecules into reactive states
New developments in ultrafast laser technology offer exciting opportunities to investigate molecules in the presence of strong fields that are applied for a short period of time. We have developed an optical centrifuge to generate molecules in states that contain large amounts of rotational angular momentum in order to investigate the chemistry and dynamics of rotationally activated molecules. The optical centrifuge is formed by combining ultrafast pulses having opposite spectral chirp. Processes of interest include rotationally-induced dissociation and isomerization and the coupling of vibrational and rotational degrees of freedom in high energy states. We are currently developing methods for real-time monitoring of the centrifuged molecules.