Measurements of Hydroxyl Radical Production in Capacitively Coupled Plasmas

In this work we report on measurements of hydroxyl radical production in capacitively coupled plasma ignited in Ar-H₂O mixture at pressures of 100-600 mTorr and radiofrequency power levels of up to 700 W. Using the absorption spectra collected with a broadband absorption spectroscopy setup equipped with a laser-driven light source, and the rotational temperatures obtained from the emission spectra, we determined OH radical densities based on HITRAN database cross-section data. Concurrently, actinometric measurements were used to estimate the production of atomic hydrogen and oxygen in the discharge. The results indicate that the production of the OH radicals is on the order of a few percent of the total water density and decreases with pressure. The increase of the plasma power leads to further dissociation of water with simultaneous rise of the atomic hydrogen and oxygen densities.