Excitation of mercury atoms in nitrogen post-discharge

F Krčma,I Soural,I Bocková,V Mazánková,A Hrdlička,V Kanický

doi:10.1088/1742-6596/516/1/012005

Abstract

The work presents results obtained during spectroscopic observations of nitrogen DC flowing post-discharges at the total gas pressure of 1000 Pa and at the discharge current of 100 mA. Mercury traces were introduced into the system using auxiliary pure nitrogen flow enriched by mercury vapor. A very low mercury concentration of 3.7 ppb was introduced into the system before the active discharge. The strong quenching of nitrogen pink afterglow was observed but no mercury lines were recorded. Moreover, the vibrational distributions of nitrogen excited states were nearly unchanged. Based on these results, the new experimental set up was created. The introduction point of mercury vapor with higher concentration of 600 ppm was movable during the post discharge up to decay time of 40 ms. Besides three nitrogen spectral systems (first and second positive and first negative), NOβ and NOγ bands, the mercury line at 254 nm was recorded at these conditions. Its intensity was dependent on the mercury vapor introduction position as well as on the mercury concentration. No other mercury lines were observed. The creation of mercury 3P1 state that is the upper state of the observed mercury spectral line is possible by the resonance excitation energy transfer form vibrationally excited nitrogen ground state N2(X1Σ+g, v = 19). The observed results should form a background for the development of a new titration technique used for the highly vibrationally excited nitrogen ground state molecules determination.

Highlights

Nitrogen post-discharges in various configurations have been subjects of many studies during last fifty years [1,2,3,4,5,6]
Populations at the selected vibrational levels are presented in figures 2–4 as a function of decay time and wall temperature
As we proposed in the kinetic model, the mercury line at 254 nm should directly reflect the concentration of its precursor, i.e. concentration of N2 (X 1Σg+, v = 19) molecules

Summary

Introduction

Nitrogen post-discharges in various configurations have been subjects of many studies during last fifty years [1,2,3,4,5,6]. There are some other strongly metastable highly excited states (a’ 1Σu- – 739 cm-1 and a 1Πg – 951 cm-1 [12]). All these states conserve the excitation energy for very long time. The excitation energy transfer during the collisions among these species as well as atomic recombination processes lead to formation of some radiative states and the visible light emission can be observed up to one second after switching off an active discharge depending on the experimental conditions, mainly on pressure and nitrogen purity.

Methods

Results

Conclusion