Emission spectra of a pulse needle-to-plane corona-like discharge in conductive aqueous solutions

We explored basic optical and electrical characteristics of a positive corona-like discharge produced in conductive aqueous solutions by periodic high-voltage pulses. Emission spectra of the discharge were acquired in a needle-to-plate electrode geometry and analysed in the UV-vis-NIR spectral range with nanosecond time resolution for the solution conductivity of 100 and 500 mu S cm(-1). The most important emission features are due to electronic excitation of H-I, O-I, O-II and OH species. We found evidence of significant time-dependent line-shape broadening of selected H-I and O-I transitions. The observed broadening is attributed to the dynamic Stark and pressure broadening mechanisms and significantly increases with the aqueous solution conductivity. Electron densities were estimated by fitting a single Voigt peak function to the observed H alpha profiles, and can reach as much as n(e) congruent to 4 x 10(18) cm(-3) (t(D) = 300 ns at 100 mu S cm(-1) solution conductivity) and n(e) congruent to 5 x 10(18) cm(-3) (t(D) = 1 mu s at 500 mu S cm(-1)). Temporal evolution of the partially resolved rotational structure of the OH emission reaches a maximum during the discharge decay, with the onset significantly delayed with respect to the streamer ignition.