Measurement of the dissociation degree of oxygen in air plasma-arc-jets

The dissociation degree of molecular oxygen in air is measured on the axis of a plasma arcjet thanks to the actinometry technique. For this purpose, a small amount of argon is introduced into the gas of interest, and two emis sion lines, one of atomic oxygen (777.3 nm) and one of argon (811.5 nm), ar e analyzed locally, together with the corresponding electron density and en ergy distribution. Then, provided that a number of assumptions are satisfie d, the dissociation degree of oxygen is proportional to the ratio of the li ne intensities. It is found to decrease from 1 at the nozzle exit down to 0 .3 at a distance of 10 cm and increase again where a shock wave is expected .