Optical diagnostics of the hollow needle to plate electrical discharge in air at atmospheric pressure

Abstract

Vibrational and rotational excitation of the N2(C3Πu) state in a DC hollow needle to plate electrical discharge at atmospheric pressure was studied by means of multichannel emission spectrometry. Vibrational distributions and rotational temperatures of the N2(C3Πu) electronic state were obtained for a negative polarity of the needle as a function of mean energy density dissipated in the discharge reactor. Vibrational excitation of the N2(C3Πu) apparently decreases with increasing energy density and the shape of vibrational distributions reflects predominant processes responsible for the N2(C3Πu) state population, i.e. electron impact excitation of N2(X1Σg+,ν) ground state and energy pooling mechanism by N2(A3Σu+) metastables. Rotational temperatures evolve in the range 1000 ÷ 1800 K and show linear increase with energy density dissipated in the discharge reactor.