Our research concentrates on elementary processes of transient reactive intermediates, with an emphasis on atmospheric and combustion chemistry. This research aims to provide fundamental and quantitative understanding of free radical chemistry by exploring a broad range of important basic and practical scientific issues.

(1) Photodissociation dynamics of small free radicals and molecules: Free radicals play dominant roles in much of chemistry, and yet their photochemical mechanisms and reactivity have not been well characterized. State-resolved photodissociation dynamics of prototypical free radicals provide benchmarks for exploring potential energy surfaces and their influences on chemical dynamics, as well as basic understanding of free radical electronic structures, thermodynamics, and decomposition mechanisms. A high-n Rydberg-atom time-of-flight technique is utilized to study photochemistry of jet-cooled free radicals generated and isolated in a supersonic beam. With a much higher resolution and sensitivity than traditional techniques, rovibrationally state-resolved translational energy and angular distributions of H-atom product channels can be obtained, and multi-dimensional dissociation dynamics of free radicals are revealed in great detail. Photochemical systems of interest include alkyl, alkyl peroxy, and alkoxy radicals, which are key intermediates in tropospheric oxidation.

(2) Laser spectroscopic detection and chemical kinetics of atmospheric transient species: in situ detection and kinetic studies of important atmospheric transient species provide fundamental knowledge of atmospheric chemis-try. Cavity ring-down spectroscopy (CRDS), a sensitive multi-pass laser absorption technique that provides long absorption path (~ 1 km) in a compact setup, is utilized as a powerful analytical tool to detect atmospheric transient species. In addition, spectroscopy and kinetics of free radicals (alkyl, alkyl peroxy, alkoxy, etc.) are studied by CRDS and laser-induced fluorescence. These studies aim to address major questions concerning kinetics, mechanisms, and products of atmospheric free radical reactions, thus providing a basis for detailed understanding of more complex problems.

(3) Mass spectrometric study of reactive intermediates in technologically important and environmentally related chemical processes: Identification of key reaction intermediates is pivotal to accessing mechanisms of important processes such as combustion. Flash pyrolysis of reaction precursors, coupled with supersonic cooling and laser photoionization/mass spectrometry, is utilized for direct observation and analysis of initial reactive intermediates.

Selected Publications

Xu, K.; Zhang, J. "Photodissociation of Vinyl Radical (C2H3) via the First Excited State: the C2H2(X1S+g) + H Channel," J. Chem. Phys. 1999, 111, 3783-3786.

Xu, K.; Amaral, G.; Zhang, J. "Photodissociation Dynamics of Ethanol at 193.3 nm: The H-atom Channel and Ethoxy Vibrational Distribution," J. Chem. Phys. 1999, 111, 6271-6282.

Chambreau, S.D.; Traeger, J.C.; Zhang, J.; Morton, T.H. "Photoionization of Methyl tert-butyl Ether (MTBE) and tert-octyl Methyl Ether (TOME) and Analysis of Their Pyrolyses by Supersonic Jet/Photoionization Mass Spectrometry," Int. J. Mass Spectrom. 2000, 199, 17-27.

Wang, L.; Zhang, J. "Detection of Nitrous Acid by Cavity Ring-down Spectroscopy," Environ. Sci. Technol. 2000, 34, 4221-4227.

Amaral, G.; Xu, K.; Zhang, J. "The H + NO2 Channels in the Photodissociation of HONO at 193 nm," J. Phys. Chem. 2001, 105, 1465-1475.

Amaral, G.; Xu, K.; Zhang, J. "UV Photodissociation Dynamics of Ethyl Radical via the Ã2A'(3s) State," J. Chem. Phys. 2001, 114, 5164-5169.

Chambreau, S.D.; Zhang, J. "VUV Photoionization Time-of-flight Spectrometry of Flash Pyrolysis of Silane and Disilane," Chem. Phys. Lett. 2001, 343, 482-488.

Chambreau, S.D.; Wang, L.; Zhang, J. "Highly Unsaturated Hydrogenated Silicon Clusters, SinHx (n = 3-10, x = 0-3), in Flash Pyrolysis of Silane and Disilane", J. Phys. Chem. 2002, 106, 5081-5087.

Wang, L.; Zhang, J. "Ab Initio Study of Reaction of Dimethyl Sulfoxide (DMSO) with OH Radical", Chem. Phys. Lett. 2002, 356, 490-496.

Zhou, W.; Yuan, Y.; Zhang, J. "Photodissociation Dynamics of 1-Propanol and 2-Propanol at 193.3 nm," J. Chem. Phys. 2003, 119, 7179-7187.

Zhou, W.; Yuan, Y.; Zhang, J. "State-to-state Photodissociation Dynamics of OH Radical via the A2S+ State: Fine-structure Distributions of the O(3PJ) Product," J. Chem. Phys. 2003, 119, 9989-9992.

Wang, L.; Zhang, J. "Theoretical Study on the Thermochemistry of Chlorinated and Fluorinated Germanes and Their Radical Fragments," J. Phys. Chem. A 2004, 108, 10346-10353.