Collisional broadening and pressure shift coefficients for the potassium D1 and D2 transitions in oxygen and carbon dioxide at high temperatures

Abstract

Collisional broadening and pressure shift parameters for the potassium resonance doublet, near 770 nm, are reported for collisions with molecular oxygen and carbon dioxide. Experiments were conducted in a reflected shock tube from 1200–2200 K and used potassium chloride (KCl) salt as the atomic potassium source. The measured absorption lineshapes were fit with Voigt profiles to infer the collisional broadening and pressure shifts. Power-law correlations were then developed to describe the pressure-normalized results as functions of temperature. Generally, the collisional broadening coefficients in oxygen agree well with theoretical predictions and are similar to those in nitrogen. Conversely, the pressure shift coefficients in oxygen differ from those in nitrogen by up to 15%. Broadening coefficients in carbon dioxide disagree with theoretical predictions by 20% or more over the range of temperatures explored in this work. These results expand the existing database of potassium lineshape coefficients, and they are expected to be useful for further development of potassium sensing diagnostics in terrestrial, Martian, and Venusian atmospheric flight studies, and in combustion systems. Other anticipated applications include interpretation of astrophysical spectroscopic observations.