Spectroscopic measurements of the electron number density, electron temperature and OH(A) rotational distribution in a liquid electrode dielectric barrier discharge

•Simultaneous determination of electron temperature and number density•Study of the Stark broadening of a neutral and two ionic Strontium emission lines•OH(A) rotational distribution estimation using Bolzmann plot method•Non-Boltzmann behavior with a superposition of two Boltzmann distributions•Higher rotational state distribution formed by an electrospray-like process

The electron temperature and number density as well as the OH(A) rotational distribution of a discharge with flowing liquid electrode and dielectric barrier coupling (a liquid electrode dielectric barrier discharge, LE-DBD) were investigated by means of optical emission spectroscopy. By using the Stark broadening of three Strontium lines, the electron number density Ne and the lower bound of the electron temperature Te can be simultaneously measured. The values obtained were Ne = (0.8 − 1.6) × 1016 cm− 3 and Te > 1.1 eV, respectively. The OH(A) rotational distribution deviates from equilibrium and can be described by a superposition of two Boltzmann distributions with T1 = (3230 ± 90) K for K ' ≤ 15 and T2 = (7300 ± 300) K for K ' ≥ 16. Consideration of the formation mechanisms of OH(A) and reaction rates suggests that the dissociative recombination of H2O+ and H3O+ is responsible for the higher rotational state distribution, where these ions can only be produced in the LE-DBD through an electrospray-like process.