Influence of Mercury Traces on Vibrational Populations of N_2 (B ^3 Pi_g) State during the Post-Discharge at Decreased Wall Temperature

lecture

English

The work presents results obtained during spectroscopic observations of DC flowing post-discharges of pure nitrogen plasma and nitrogen plasma containing very low mercury traces of about 3.7 ppb. The decaying plasma up to 50 ms was studied by the emission spectroscopy in the range of 300 - 850 nm. The discharge tube around the observation point (3 cm) was immersed in liquid nitrogen. The nitrogen spectral systems and NO-beta bands were identified, but no mercury lines were observed in the measured spectral region. The total gas pressure was 700 Pa and the discharge current was kept at 150 mA. The relative vibrational populations of N_2 (B ^3 Pi_g) state were calculated in the dependence on the post-discharge time. As the uncontrolled oxygen traces were recorded in the mercury flow, the experiment with a nitrogen-oxygen mixture at the same discharge conditions was studied, too. The results showed state specific influence of the mercury traces. The kinetic explanation can be done through a strong depopulation of the level N_2 (X ^1_g^+, v = 19) (creation of mercury ^3 P_1 state) and levels N_2 (X ^1 Sigma_g^+,v = 28) or N_2 (A ^3 Sigma_u^+,v = 4) (creation of mercury ^1 S_0 state). Both mercury states are origins of the UV light emission (254 and 185 nm, resp.) that could not be detected in our contemporary experimental setup.

nitrogen post-discharge, pink afterglow, post-discharge kinetics, optical spectroscopy, mercury traces

KRČMA, F.; HRDLIČKA, A.; KANICKÝ, V.; OTRUBA, V.; KRÁSENSKÝ, P.

3. 4. 2007

Beverley