uv continuum emission and diagnostics of hydrogen-containing nonequilibrium plasmas

Abstract

For the first time the emission of the radiative dissociation continuum of the hydrogen molecule (a 3 Σ + g → b 3 Σ + u electronic transition) is proposed to be used as a source of information for the spectroscopic diagnostics of non-equilibrium plasmas. The detailed analysis of excitation-deactivation kinetics, rate constants of various collisional and radiative transitions and fitting procedures made it possible to develop two new methods of diagnostics of: (1) the ground X 1 Σ + g state vibrational temperature T vib from the relative intensity distribution, and (2) the rate of electron impact dissociation (d[H 2 ]/dt) diss from the absolute intensity of the continuum. The known method of determination of T vib from relative intensities of Fulcher-α bands was seriously corrected and simplified due to the revision of d → a transition probabilities and cross sections of d ← X electron impact excitation. General considerations are illustrated with examples of experiments in pure hydrogen capillary-arc and H 2 +Ar microwave discharges. In pure H 2 plasma the values of T vib obtained by two independent methods are in rather good accordance (T vib =3000-5000 K). In the H 2 +Ar microwave plasma it was observed for the first time that the shape of the continuum depends on the ratio of the mixture components. Absorption measurements of the population of the 3s 2 3p 5 4s levels of Ar together with certain computer simulations showed that the Ar*→H 2 excitation transfer plays a significant role. In our typical conditions (power flux: 4 W cm −2 , pressure p = 0.5 mbar, H 2 :Ar=1:1) the following values were obtained for the microwave discharge: (d[H 2 ]/dt) diss ≈ 2.5 − 5 · 10 17 cm −3 s −1 . The contribution of the excitation transfer is about 10-30% of the total population of the a 3 Σ + g state.

Quantification of the VUV radiation in low pressure hydrogen and nitrogen plasmas

“…The simulation of the continuum emission implies the consideration of a repulsive state and thus wavelength dependent transition probabilities assigned to the ro-vibrational quantum number of the upper state. Simulation of the continuum emission is applied successfully at low temperature plasmas for plasma diagnostic purposes; in particular, it has been shown that the vibrational population determines the shape of the continuum emission, whereas the intensity is sensitive to the electron density and temperature [29,30]. Figure 4 shows the spectrum of a hydrogen plasma at a pressure of 3 Pa measured with the VUV spectrometer.…”

Optimal values of rovibronic energy levels for triplet electronic states of molecular deuterium

“…Optimal values of the rovibronic levels for the triplet electronic states corresponding to principle quantum numbers n = 2, 3 of the united atom are listed in table III. Radiative transitions between those levels are located in visible part of spectra, which is most convenient for spectroscopic studies of non-equilibrium gases and plasmas [4,5]. The expanded version of the table III including all 1050 optimal level values is presented in [46].…”

Langmuir probe diagnostic studies of pulsed hydrogen plasmas in planar microwave reactors

“…The analysis of excitation processes such as the determination of the gas temperature and of the degree of dissociation in plasmas containing molecular feed gases, e.g. hydrogen or diborane, was also examined using emission spectroscopy [13][14][15]. Recently, this type of reactor has been used to investigate the chemistry and kinetics in plasmas with admixtures of hydrocarbons and other reactive gases by infrared absorption spectroscopy [16,17].…”