Abstract
The N2 (C 3Πu) and N2 (B 3Πg) triplet states are studied in the positive column of a nitrogen dc pulsed discharge by optical emission spectroscopy. Time variations of all vibrational levels are observed during a 700 µs pulse duration in a pressure range from 0.05 to 4 Torr. Even if the current remains constant during the pulse, the bands intensities emitted from the triplet states change during the pulse. According to the state and the vibrational level, we observe an increase or a decrease of line intensities as a function of pressure. It is pointed out that for N2 (B 3Πg) time variations are not similar for low and high vibrational levels. From the observation of individual vibrational levels, time evolution of vibrational distributions (VDs) are measured for N2 (B 3Πg) and N2 (C 3Πu). From these VDs a vibrational temperature is deduced. For a 4 Torr pressure, the deduced vibrational temperature increases from 5000 to 9000 K for N2 (B 3Πg) and from 3000 to 9000 K for N2 (C 3Πu). This vibrational temperature is representative of the temporal evolution of the plasma and, even after 700 µs, a steady state is not reached.
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