Population Density Measurements in a Supersonic Freejet Expansion Flow of an O₂-seeded Ar Plasma

Abstract

The population densities of O(3p³P) and O(3p⁵P) were measured along the freejet centerline of an O₂-seeded Ar plasma, which was such that oxygen gas was seeded into a pre-ionized argon plasma. The ratio of the measured population densities of the 3p³P and 3p⁵P states was compared with the predicted ratio, which was determined from a steady state population assumption of O(3p⁵P), over the whole region of the freejet. The comparison showed that on the condition Nₑ=1.8×10¹³-1.7×10¹²cm⁻³ Tₑ= 3000-900 K and p＝48-0.19 Pa, the 3p⁵P state is populated by electron-collisional de-excitations of the 3p³P state, rather than by quenching of the 3p³P state by the ground state argon. Further, the 3p⁵P state is de-populated by electron-collisional de-excitations rather than by radiative de-excitations.