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John Hershberger

Experimental Physical Chemistry, Laser Kinetics

The detailed kinetics and dynamics of elementary gas-phase chemical reactions is a topic of great interest in chemistry, with applications in atmospheric chemistry, combustion science, and modeling of chemical vapor deposition processes. A major research area in our group is the elucidation of mechanisms in the combustion chemistry of nitrogen.  Many nitrogen-containing radicals such as CN, NCO, NO, etc. are formed in combustion environments and ultimately lead to nitrogen oxide emissions, a major source of air pollution. Strategies to control nitrogen oxide (NOx) emissions include several aftertreatment processes such as the thermal De-NOx and NO-reburning mechanisms. Our understanding of these processes relies on detailed kinetic models, which in turn rely on elementary kinetic information such as that obtained in our laboratory. We use Nd:YAG and excimer lasers to initiate chemical reactions, and high-resolution infrared diode lasers and visible dye lasers to probe reactants and products with an extremely high degree of specificity. Many reactions of importance in combustion chemistry, such as NH2 + NO2, HCCO + NO, CH + NO, CN + NO2, etc., have several possible product channels, some involving non-intuitive molecular rearrangements via cyclic transition states. Major goals in our laboratory include the quantitative determination of product branching ratios as well as total rate constants. Past studies have emphasized infrared laser probes, but we have also occasionally used laser-induced fluorescence (LIF) to detect some species. Although less generally applicable than infrared absorption, LIF offers extremely high sensitivity in the detection of certain radical species. We have also, in some cases, performed high level ab initio calculations in order to characterize the potential energy surfaces of these reactions.

In recent years we have become interested in the detailed chemistry of fulminic acid (HCNO). This is the less stable isomer of isocyanic acid, HNCO. Fulminic acid is produced in combustion in the reaction of HCCO + NO, where HCCO can come from acetylene oxidation. Previous to our work, no literature existed on the kinetics of fulminic acid chemistry. We study several radical-molecule reactions involving HCNO, including CN+HCNO, NCO+HCNO, O+HCNO, etc. By using infrared detection of molecular products, we have been able to substantially map out the chemistry of this important molecule. Ongoing work includes study of photochemical pathways of this molecule as well. Other recent work includes investigations of the chemistry of the NCCO radical, and ongoing work on the HCC radical.

Selected Publications

Product Branching Ratio of the HCCO+NO Reaction”, K.T. Rim and J.F. Hershberger, J. Phys. Chem. A 104, 293 (2000).

Recent Progress in Infrared Absorption techniques for Elementary Gas Phase Reaction Kinetics”, C. Taatjes and J.F. Hershberger, Ann. Rev. Phys. Chem. 52, 41 (2001).

Kinetics of NCN Reactions”, R.E. Baren and J.F. Hershberger, J. Phys. Chem. A. 106, 11093 (2002).

“Ab Initio Study of the HCCO+NO2 Reaction”, J.P. Meyer and J.F. Hershberger, Chem. Phys. 325, 545 (2006).

Kinetics of the OH+HCNO Reaction”, W. Feng, J.P. Meyer, and J.F. Hershberger, J. Phys. Chem. A 110, 4458 (2006).

“Theoretical Study of the Reaction of O(3P) with HCNO”, W. Feng and J.F. Hershberger, Chem. Phys. Lett. 457, 307 (2008).

“A Re-investigation of the Branching Ratio of the CN+O2 Reaction”, W. Feng and J.F. Hershberger, J. Phys. Chem. A 113, 3523 (2009).

“Kinetics and Mechanism of the NCCO + NO Reaction”, W. Feng and J.F. Hershberger, J. Phys. Chem. A, 114, 6843-6949 (2010).

“Kinetics of the CN + CS2 and CN + SO2 Reactions”, W. Feng and J.F. Hershberger, J. Phys. Chem. A 115, 286-290 (2011).

“Kinetics of the NCCO + NO2 Reaction”, W. Feng and J.F. Hershberger, J. Phys. Chem. A 115, 12173-12183 (2011).

“Product Channels of the CN + HCNO Reaction”, W. Feng and J.F. Hershberger, J. Phys. Chem. A 116, 10285-10292 (2012).

“Experimental and Theoretical Study of the Product Channels of the C2H + NO Reaction”, W. Feng and J.F. Hershberger, J. Phys. Chem. A 117, 3585-3592 (2013).


BS, University of California, Santa Barbara, 1982
PhD, Yale University, 1986
Postdoctoral Fellow, Columbia University, 1986-1989

Office: 101B Ladd

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