Negative ion species in atmospheric-pressure helium dc glow discharge produced in ambient air

Experimental investigation on negative ions in atmospheric-pressure plasmas is insufficient to date. In this work, we examined negative ion species in atmospheric-pressure helium dc glow discharge produced in ambient air by laser photodetachment spectroscopy, where the pulsed increase in the discharge current was measured as a function of the laser wavelength. A major negative ion species was O(-)which was originated from molecular oxygen in the ambient air. OH(-)and Cl(-)were also major negative ion species when we used an NaCl solution as the cathode of the dc discharge.O2-<iwas minor in comparison with O-, and H(-)was negligible. The production process of OH(-)was not dissociative electron attachment to H2O. The experimental results are consistent with the dominant production of OH(-)due to dissociative electron attachment to H2O2.