Our research involves trying to understand chemical reactivity on a microscopic quantum-state resolved level. We focus on isolated molecules in the gas-phase to develop a detailed description of the factors which influence the rates, energy disposal, and final products in a reaction. In order to address these issues we use lasers to carefully control the preparation of excited molecules and to probe all the properties of the reaction products. Our specific interests include understanding atmospheric photochemistry, the tropospheric oxidation of biogenic hydrocarbons, and laser diagnostic development for flow field characterization. The laboratory contains equipment to perform state-of-the-art experiments in chemical dynamics and kinetics and is associated with several interdisciplinary University Research Centers. Our photochemistry experiments combine molecular beam and state-resolved ionization techniques with position-sensitive ion imaging to determine the identity and energy content of photochemical products in the absence of secondary collisions. Studies focus on the photodissociation of jet-cooled radicals of atmospheric relevance and preliminary results have already stimulated collaboration with several theoretical groups. The experiments provide a stringent test for modern theory and allow assessment of the impact that the photochemistry has on atmospheric modeling.
Our group is also interested in understanding tropospheric chemistry. One effort involves the study of the oxidation of tropospheric biogenic hydrocarbons which has major implications for local and regional air quality. In recent years it has become increasing evident that refining our understanding of atmospheric chemistry of hydrocarbons requires detailed characterization of the elementary reaction mechanism that must involve combined experimental and theoretical studies. Our approach is based on this philosophy, combining state-of-the-art experimental techniques, chemical ionization mass spectrometry and laser photolysis/laser induced fluorescence, with modern ab initio and rates theory calculations to obtain a comprehensive and predictive description of hydrocarbon oxidation chemistry. Ultimately our goal is to predict ozone formation on the regional and global scales as well as the long-range transport of NOx. Recently we have extended our atmospheric studies to include the development and application of field instrumentation for measuring trace radical species.
Finally, our group is involved in collaborative efforts with Rodney Bowersox (Aerospace Engineering) and the National Aerothermochemistry Laboratory at Texas A&M University. We are currently developing novel laser diagnostics for velocity and basic state characterization in hypersonic flows. This research focuses on optical characterization of high speed (hypersonic) flows; measurement of freestream turbulence, measurement of internal energy distributions and relaxation of non-thermal equilibrium (NTE) distributions, surface ablation and reactivity, and laser induced NTE driven turbulence. These measurements require the application of state-of-the art laser diagnostic techniques such as coherent anti-Stokes Raman spectroscopy (CARS), Raman, and two-line planar laser induced fluorescence (PLIF).
M. P. Grubb, M. L. Warter, H. Xiao, S. Maeda, K. Morokuma, and S. W. North: "No Straight Path: Multistate Roaming as the Only Route for the NO3 → NO + O2 Reaction" Science, 355, 1075 (2012).
R. Sanchez-Gonzalez, D.Y. Kim, A. J. Tindall, J. Hofferth, R. Srinivasan, R. D. W. Bowersox, and S. W. North: "Repetitively Pulsed Hypersonic Flow Apparatus for Diagnostic Development" AIAA Journal 50, 691 (2012).
M. P. Grubb, M. L. Warter, and S. W. North: "Stereodynamics of Multistate Roaming" Phys. Chem. Chem. Phys. In press (2012).
R. Sanchez-Gonzalez, R. D. W. Bowersox, and S. W. North: "Simultaneous Velocity and Temperature VENOM Measurements in Gaseous Flow Fields: A Comprehensive Study" Applied Optics, 36,196 (2012).
S. W. North: "Roaming in the Dark" Nature Chemistry, News and Views, 3, 504 (2011).
M. P. Grubb, M. L. Warter, C. D. Freeman, N. A. West, K. M. Usakoski, K. M. Johnson, J. A. Bartz, and S. W. North: "A Method for the Determination of Speed-Dependent Semi-Classical Vector Correlations from Sliced Image Anisotropy", J. Chem. Phys. 135, 094201 (2011).
M. P. Grubb, M. L. Warter, K. M. Johnson, and S. W. North: "Ion Imaging Study of NO3 Radical Photodissociation Dynamics: Characterization of Multiple Reaction Pathways", J. Phys. Chem. 115, 3218 (2011).
B. Ghosh, A. Bugarin, B. T. Connell, and S. W. North: "Isomer-Selective Study of the OH-Initiated Oxidation of Isoprene in the Presence of O2 and NO: II. The Major OH-Addition Channel" J. Phys. Chem. A, 114, 2553 (2010).
E. E. Greenwald, B. Ghosh, K. C. Anderson, K. S. Dooly, P. Zou, T. Selby, D. L. Osborn, G. Meloni, C. A. Taatjes, F. Goulay, S. R. Leone, and S. W. North: "Isomer-Selective Study of the OH-Initiated Oxidation of Isoprene in the Presence of O2 and NO: I. The Minor OH-Addition Channel" J. Phys. Chem. A, 114, 904 (2010).