Identification and imaging of hot O2 (v?=2, 3, or 4) in hydrogen flames using 193 nm- and 210 nm-range light

Abstract

Some simple molecules can be excited by light within the tuning ranges of ArF (193–194 nm) and KrF (247.8–248.8 nm) excimer lasers and their fluorescence has been previously used for imaging. Additional wavelength ranges should become available by Raman shifting. As a demonstration, we present excitation and fluorescence spectra from hot O2 obtained (a) with tunable 193 nm-range light and (b) with that light shifted into the 210 nm range. All measurements are via predissociative upper states. In the 193 nm range, results are compared with those of Andresen's group. In the 210 nm range, the light is tuned to various excitation wavelengths in the (5 ← 3), (8 ← 4), and (7 ← 4) bands of the B–X transition. The (7 ← 4) excitations are well separated and the (7 → v″) fluoresence spectrum is in accord with Franck-Condon calculations. The wavelengths tend to overlap for the (5 ← 3) and (8 ← 4) excitations and the fluorescence is weaker. State-specific two-dimensional fluorescence images of an H2-O2 flame are obtained in both wavelength ranges to illustrate the use of the method.