Revisiting spontaneous Raman scattering for direct oxygen atom quantification

In this Letter, the counterintuitive and largely unknown Raman activity of oxygen atoms is evaluated for its capacity to determine absolute densities in gases with significant O-density. The study involves CO2 microwave plasma to generate a self-calibrating mixture and establish accurate cross sections for the 3𝑃2↔3𝑃1 and 3𝑃2↔3𝑃0 transitions. The approach requires conservation of stoichiometry, confirmed within experimental uncertainty by a 1D fluid model. The measurements yield 𝜎𝐽=2→1=5.27±rand:0.17sys:0.53×10−31cm2/sr and 𝜎𝐽=2→0=2.11±rand:0.06sys:0.21×10−31cm2/sr, and the detection limit is estimated to be 1×1015cm−3 for systems without other scattering species.