219 Parkman Avenue
Pittsburgh, PA 15260
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Spectroscopy and Chemical Kinetics
Professor Golde's group is using experiment and theory to learn about the mechanisms of elementary reactions of atoms, radicals, ions and small molecules in the gas phase. Two separate areas are involved: reactions of ions and radicals of relevance to the chemistry of combustion and of the atmosphere; and reactions and energy-transfer processes involving electronically excited species of relevance to gas lasers, plasmas, and processes in the upper atmosphere. To characterize these processes, we measure rate constants and products of reactions and probe the energy disposal in exothermic processes. The discharge-flow technique is used, in which the reaction of interest is isolated from possible interfering reactions, and its progress is followed via a variety of very sensitive, in situ detection techniques, including emission spectroscopy, atomic resonance fluorescence, laser-induced fluorescence, and mass spectrometry.
The electronically excited species have been found to induce several remarkable reaction channels. For instance, in collisions with halogen molecules, excited Ar, Kr and Xe atoms form diatomic noble gas halide "excimer" molecules. These have strong chemical bonds and give rise to characteristic light emission, which has been exploited in a new class of laser.
The lowest excited state of N2 is very unreactive towards molecules such as H2, CH4 and H2O, but reacts at nearly every collision with such molecules as NH3, H2S and H2O2. In explaining this behavior, we have been able to predict, confirm experimentally, and finally verify by ab initio calculations, that for certain reagents the reactivity of the excited electronic state is enhanced dramatically by small amounts of vibrational energy in the N2 molecule.
The chemistry of alkenes, of critical importance in air pollution, appears to involve intricate pathways, via energy-rich bound intermediates, which are presently very poorly understood. We are investigating the products of reactions of electronically-excited species with representative alkenes such C2H4, C2F4 and CF2CFH. The latter two reactions are prolific sources of the CF2 species.
Reaction with an electron is the ultimate fate of positively-charged ions. These reactions are extraordinarily fast, but the neutral products are largely unstudied. By analogy with our other work, we expect extensive dissociation of the molecule, possibly accompanied by light emission from electronically-excited fragments. Ions of interest include simple species such as O2+ and H2O+, protonated molecules such as H3+ and CH5+3O+H2O and NH4+NH3.