Resonance absorption measurements of atom concentrations in reacting gas mixtures. VI. Shapes of the vacuum ultraviolet oxygen (3S–3P) resonance triplet from microwave sources and empirical calibration in a shock tube

Publisher Website
Google Scholar
Abstract
Spectral line profiles of the atomic oxygen triplet 3S1–3P2,1,0 emitted from microwave discharges in O2–He mixtures containing 0.1% O2 were measured in the 43rd order using a 2 m vacuum Czerny‐Turner scanning spectrometer under three different lamp conditions. The profiles varied from nearly Gaussian to highly self‐absorbed. The line shapes were accounted for by the amount of light absorbed by ground state oxygen atoms within the lamp. Experiments were carried out to calibrate the microwave discharge lamp for analysis of oxygen atoms using oxygen resonance triplet absorption. Known concentration of O atoms were produced in the temperature range 1950–2600 K in a shock tube by the complete dissociation of dilute (1–20 ppm) mixtures of N2O in Ar and related to the fraction of light absorbed. It was found that the ratios of the intensities of the oxygen components, measured using a low‐resolution monochromator, can be used to obtain resonably accurate calibration curves. Kinetic data obtained on N2O dissociation as a part of our calibration experiments in the temperature range 1519–2408 K are also presented; the results are consistent with the correlations of Baulch et al. It was confirmed that O atom concentrations during calibration experiments were determined by stoichiometry, and not by the kinetics of N2O dissociation.