Assistant Professor of Chemistry
Physical chemistry, reaction dynamics
Postdoctoral Researcher, the University of California, Berkeley
Ph.D., Physical chemistry, the University of Chicago
B.S., Chemistry, Wayne State University
Characterizing the Ro-vibrational Distribution of CD2CD2OH Radicals Produced via the Photodissociation of d4-2-bromethanol, C.C. Womack, R. Booth, M. Brynteson, L.J., Butler, and D. Szpunar, J. Phys. Chem. A., 115 14559 (2011).
Chloroacetone Photodissociation at 193 nm and the Subsequent Dynamics of the CH3C(O)CH2 Radical—An Intermediate Formed in the OH + Allene Reaction en Route to CH3 + Ketene, B. W. Alligood, B. L. Fitzpatrick, D. E. Szpunar, and L. J. Butler, J. Chem. Phys. 134, 054301 (2011)
Modeling the Rovibrationally Excited C2H4OH Radicals from the Photodissociation of 2-Bromoethanol at 193 nm, B. J. Ratliff, C. C. Womack, X. N. Tang, W. M. Landau, L. J. Butler, and D. E. Szpunar, J. Phys. Chem. A 114, 4934 (2010)
Determining the CH3SO2 → CH3 + SO2 Barrier from Methylsulfonyl Chloride Photodissociation at 193 nm Using Velocity Map Imaging, Britni J. Ratliff, Xiaonan Tang, Laurie J. Butler, David E. Szpunar and Kai-Chung Lau, J. Chem. Phys. 131, 044304 (2009).
Velocity Map Imaging of Atmospherically Important Radicals and their Photolytic Precursors
My research interests lie in the area of photodissociation dynamics. This field of study examines the details of reactions that involve the rupture of a bond following the absorption of light. In particular, the field of photodissociation dynamics hopes to answer questions such as, how does the absorbed photon break the bond? What is the lifetime of the species upon absorption of the photon? What are the main fragments that the molecule breaks into? How is the energy of the photon partitioned to the fragments?1 Can the newly-produced fragments go on to dissociate (break apart) themselves (i.e. can the fragments undergo secondary dissociation)?
In my lab, we focus on the energetics of these secondary dissociation processes. We use photodissociation of a halogenated species to form radical intermediates found in atmospherically important reactions.2 These newly-formed radicals then undergo secondary dissociation. The experiments can shed light on the barrier heights in these atmospherically important reactions, as well as the inter- and intramolecular forces involved in these reactions.
Briefly, a molecular beam of these halogenated radical precursors is crossed with the output of an ultraviolet laser to initiate dissociation, producing the halogen atom (2Pj) and its momentum-matched radical fragment. The nascent halogen atoms are selectively ionized using resonance enhanced multiphoton ionization (REMPI), and detected using the velocity map imaging (VMI) technique.3 The translational energy distribution (P(ET)) derived from these halogen atoms is then calculated, yielding insight on the primary photodissociation reaction. Any nascent radical fragments are examined using VMI with vacuum ultraviolet (VUV) photoionization at 118nm. Due to momentum-matching, the resulting P(ET) derived from any stable nascent radicals should be identical to that derived from the halogen products. Any radicals that are not stable (i.e. have energies exceeding any barrier heights to dissociation) will dissociate and not be represented in the radical-derived P(ET). In other words, high-velocity radicals (with low internal energies) will be represented, while those slower radicals (with higher internal energies) will not be represented. Determining where the halogen-derived and radical-derived P(ET)s diverge signals the translational energy at which radicals become unstable. Energy conservation is then invoked to determine at which internal energy the radicals become unstable, yielding the barrier height.
- R. Schinke, Photodissociation Dynamics, Cambridge University Press, New York, NY (1993)
- J. Phys. Chem. A 115 14559-14569 (2011); J. Chem. Phys. 131 044304 (2009).
- Rev. Sci. Instrum., 68 3477–3484 (1997)