Tunable excimer lasers are used to obtain 2-D images of molecular (and some state-specific) density distributions inside a cylinder of a modified four-cylinder in-line engine that has optical access. Natural fluorescence (i.e., without a laser) is used for some OH pictures, normal laser-induced fluorescence (LIF) for those of NO and of the isooctane fuel, and laser-induced predissociative fluorescence (LIPF) for other OH pictures and for those of O(2). Relevant spectroscopy is done to find the laser and fluorescence frequencies needed to measure isolated species. LIPF works well at high pressures, is state specific, and is ideally suited to follow turbulent processes. No similar measurements in engines have been previously reported. Pictures are taken in succeeding engine cycles. Their sequence is either at a particular point of the engine's cycle to show cyclic fluctuations, or at succeeding portions of the cycle to illustrate the progress of the gasdynamics or of the combustion.

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Dispersed LIF spectra of O 2 in the Schumann-Runge band were measured with a modified tunable ArF laser in a flame. Spin-state selective predissociation of the B state was directly observed in fluorescence excitation spectra, revealing the relative coupling matrix elements of the triplet components to the manifold of repulsive states. Such data determines the symmetries of the important predissociating curves for each observed B-state vibrational level and shows that past interpretation of absorption linewidth data is in error. Due to the fast predissociation, quench-free emission spectra arising from laser prepared single rovibronic levels in the B state were observed even in an atmospheric flame. Fluorescence to X-state vibrational levels as high as v" = 35 was observed and relative emission probabilities were derived.

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