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. 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, which is confirmed within experimental uncertainty by a 1D fluid model. The measurements yield σ(J=2→1)=5.27±(sys: 0.42)(rand: 0.16)×10¯³¹ cm²/sr and σ(J=2→0)=2.11±(sys: 0.16)(rand: 0.06)×10¯³¹ cm²/sr and the detection limit is estimated to be 1×10¹⁵ cm¯³ for systems without other scattering species.