O2 rotational temperature measurements by coherent microwave scattering from REMPI

This Letter reports non-intrusive local rotational temperature measurements of molecular oxygen, based on coherent microwave scattering (Radar) from Resonance Enhanced Multi-Photon Ionization (REMPI) in air and in pure oxygen with subsequent analysis of the rotational state distribution. Rotationally resolved 2 + 1 REMPI spectra of molecular oxygen (C3Π (v = 2) ← X3Σ (v′ = 0)) at different temperatures have been obtained by Radar REMPI. Rotational temperatures have been determined from the Boltzmann plots of various experiments. The overall measurements have an accuracy of ∼60 °C in the pure oxygen and ∼50 °C in the room air, with experiments conducted up to 500 °C.