James G. Anderson
James G. Anderson
- Philip S. Weld Professor of Atmospheric Chemistry
The Anderson research group bridges three domains within physical chemistry:
- chemical reactivity viewed from the microscopic perspective of electronic structure, molecular structure, and reactivity of radical-radical and radical-molecule systems, particularly those radicals that are primary or secondary products of photodecomposition in the hydrogen, halogen, oxygen, sulfur, carbon, and nitrogen families;
- chemical catalysis sustained by free-radical chain reactions that dictate the macroscopic rate of chemical transformations in the Earth's stratosphere and troposphere; and
- mechanisms linking chemical, dynamical and radiative processes in the atmosphere that dictate atmospheric structure and temporal change on a global scale. Studies are carried out both in the laboratory, in which elementary processes can be isolated and understood at a fundamental level, and within natural systems, in which reaction networks and radiative/dynamical processes are diagnosed by establishing cause and effect using simultaneous, in situ detection of interrelated free radicals, observations of tracers that map the patterns of atmospheric motion and radiation measurements that define the spectrally and spatially resolved radiance within the atmosphere that are essential for an understanding of climate.
Laboratory studies emphasize gas phase radical-radical and radical-molecule reactions using laser magnetic resonance, metal-atom laser-induced fluorescence, atomic and molecular resonance fluorescence, and high-resolution infrared absorption techniques. Theoretical studies use electronic structure calculations in concert with experimental results to define the potential surface over which the reaction takes place and to identify the specific mechanisms driving the reaction.
The objective of these combined studies is to (1) define the reaction pathways leading through the intermediate complex to the reaction products; (2) investigate the products of and the rate of reaction over a broad range of stabilizing collision frequencies; (3) examine reaction pathways following stabilization of the complex; and (4) design experiments that will define the geometry of the intermediate complex. A key objective is to develop a theoretical structure that provides predictive power for a wide variety of systems.
Chemical studies in the Earth Sciences constitute an important component of the research. In the past few years, it has become clear that a pattern of chemical change of the Earth's oceans, atmosphere, and terrestrial biochemical systems exceed natural bounds on CH4, CO2, chlorofluorocarbons, and O3. The mechanism is different in each case. Experiments to dissect the response of the global system to these changes are flown on aircraft to obtain simultaneous, in situ, measurements of selected free radicals.