SPECTRAL-ANALYSIS OF THE LIGHT EMITTED BY STREAMERS IN HYDROCARBON LIQUIDS

This paper presents the results of a spectroscopic study from 200 to 8 50 nm of the light emitted by streamers initiated in cyclohexane and n -pentane under step voltage in point-plane geometry. Experimental spec tra of the light emitted by bush-like and filamentary streamers are co mposed of the H-alpha-Balmer line, the C-2 Swan band system and a back ground continuum. The diagnostic method we used for evaluating rotatio nal and vibrational temperatures of excited C-2 in streamers was first tested on high-pressure corona discharges in nitrogen. For streamers in cyclohexane and n-pentane, it was impossible to determine the rotat ional temperature of C-2 and consequently the effective temperature of molecules in the streamer. Moreover, we found that vibrational popula tions of excited C-2 do not follow Boltzmann statistics. This indicate s that excitation processes are due to chemical reactions. Electron de nsities deduced of the Stark broadening of H-alpha are in the range 4x 10(16) to 7x10(16) cm(-3) for filamentary streamers and 2 to 6x10(17) Cm-3 during the breakdown phase. For slow bush-like streamers, the ele ctron density is not measurable.