Chemical dynamics of highly excited molecules; collisional energy transfer and chemical reactions of activated molecules; high-resolution transient optical probing; trajectory calculations of molecular collisions; dynamics of molecules in extreme rotational states created in an optical centrifuge, behavior of molecules in strong optical traps.
American Chemical Society (ACS); American Association for the Advancement of Science (AAAS), Fellow; American Physical Society (APS); Sigma Xi (ΣΞ); Fellow American Association for the Advancement of Science; Optical Society of America; National Organization for the Professional Development of Black Chemists and Chemical Engineers (NOBCChE), Alpha Chi Sigma (AXE), professional chemistry fraternity..
Major Recognitions and Honors
Significant Professional Service and Activities
Arnold and Mabel Beckman Foundation: Beckman Scholar Program Executive Committee (2007-2011); Beckman Scholar Program Advisory Panel (2001-2004, 2006-2007). Department of Energy: Workshop on Predictive Simulations of Combustion (2011); Fellowship Review Panel (2010); Workshop on Basic Research Needs for Clean and Efficient Combustion of 21st Century Transportation Fuels (2006); Visiting Review Committee for Chemical Sciences Division, Argonne National Laboratory (2001); Graduate Research Fellowship Review Panel (2009); Energy Frontier Research Panel (2009). National Science Foundation: Chemical Instrumentation Review Panel (2010); Graduate Research Fellowship Review Panel (2009); Visiting Review Committee for Environmental Molecular Science Institute at the University of California Irvine (2004); Chemical Instrumentation Review Panel (2000); Committee of Visitors Triennial Review (1998). American Chemical Society: Scientific Committee for 2012 International Chemistry Olympiad (2010-2012); Organizer of Symposium on “Highly Excited States: Relaxation, Reactions and Structure” (1996). American Physical Society: Program Committee, Division of Atomic, Molecular and Optical Physics (DAMOP) (2003-2006); Organizer of Symposium on “Molecules in Strong Optical Fields” (May 2007). NASA: Workshop on Mass Independent Fractionation (2011). American Association of University Women: Fellowship and Grant Selection Panel (2008-2011); Board Member, Telluride Science Research Center (2012-2015); Division of Chemical Physics, American Physical Society, Nominating Committee (2012-2013); Editorial Board of Atoms, an international journal of scientific studies related to all aspects of the atom (starting 2012)
13 PhD students, 29 undergraduate students (14 of whom entered graduate programs), 7 postdoctoral fellows, 4 high school research interns and 4 visiting professors; 4 students have received Ph.D. degrees and 4 students received M.S. degrees.
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.
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 a high power 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.