A. Denat et al., SPECTRAL-ANALYSIS OF THE LIGHT EMITTED BY STREAMERS IN HYDROCARBON LIQUIDS, IEEE transactions on dielectrics and electrical insulation, 5(3), 1998, pp. 382-387
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.