A novel method for fast and robust calculation of Boltzmann plots from molecular spectra is presented. Its use is demonstrated on the OH(A-X) spectrum near 310 nm. A limitation of the method is identified: for overlapping spectra of the OH(A-X) and N2(C-B, Δv = 1) band sequence, the calculation may often fail due to insufficient number of measured points. This is solved by introducing experimentally determined bounds for the N2(C) rotational distribution. Three cases are presented: (i) with undisturbed OH(A-X) emission, (ii) with strong emission of N2(C-B) in the said spectral range, and (iii) with weak but not negligible nitrogen emission. In case (ii), the data in the spectral range 306–320 nm are sufficient for the analysis. In case (iii), information from another spectral range with undisturbed N2(C-B) emission is necessary. These illustrate all relevant cases often encountered in laboratory plasmas. The calculated Boltzmann plots are not further analyzed in this article but can be used for development and validation of kinetic models with rotational resolution. The implementation of the reported method using the massiveOES software package written in the Python language is available in the supplementary material.

The active screen plasma nitrocarburizing technology significantly reduces the risk of cementite precipitation in the compound layer of nitrocarburized materials and of soot production compared to conventional plasma nitrocarburizing. In a laboratory-scaled plasma nitriding monitoring reactor, PLANIMOR, using an active screen made of carbon, low-pressure pulsed dc N 2 -H 2 plasmas have been studied by infrared laser absorption spectroscopy (IRLAS) techniques. Applying IRLAS, using tunable diode lasers (TDL) and a quantum cascade laser (QCL) as radiation sources, the evolution of the concentrations of eight stable molecular reaction products, C 2 H 2 , C 2 H 4 , CH 4 , HCN, NH 3 , CO, C 2 H 6 , and C 2 N 2 , and of the CH 3 radical, have been monitored. By using the line ratio method, the rotational temperatures of HCN and CO could be determined in a range of 300-400 K and 300-500 K, respectively. Analysing the profile of the CH 3 Q(3-3) absorption line, the gas temperature of this radical, i.e. the temperature in the vicinity of the plasma zone, has been found to range between 400-800 K. The concentrations of the detected molecular reaction products were found to be in the range of 10 12 -10 16 molecules cm −3 with HCN and NH 3 as the most abundant reaction products. Additionally, the respective conversion efficiencies to the product molecules (R C ≈5×10 12 -2×10 16 molecules J −1 ) have been determined for different mixing ratios of N 2 :H 2 in the feed gas and plasma power values. Taking into account the concentrations of all carbon-containing species, a maximum of the carbon combustion of the screen material of up to 96 mg h −1 has been found for a N 2 -H 2 ratio of 1:1 and the highest plasma power of the screen of P screen =106 W.

We study the origin of filamentary patterns in a sinusoidally driven surface barrier discharge at high over-voltage in atmospheric pressure air. Using a time-correlated single-photon counting based optical emission spectroscopy, we reveal ultrafast processes within generated discharges in both polarities of the applied voltage. For negative polarity, we observe initiation of complex streamer cascade which emerges far from the bare cathode. This event is responsible for long filamentary structure detected by an intensified CCD camera and transfers an exceptionally large electrical charge. It constitutes another, previously unknown, mechanism contributing to the charge-transfer equilibrium in studied periodical discharge. The revealed process leads to the formation of an intense cathode spot, a critical condition for plasma-transition into a highly ionised state.

The active screen plasma nitrocarburizing technology is an improvement of conventional plasma nitrocarburizing by providing a homogeneous temperature distribution within the workload and reducing soot formation. In this study, an industrial-scale active screen (AS) made of carbon-fibre-reinforced carbon serves as the cathode as well as the carbon source for the plasma-chemical processes taking place. The pulsed dc discharge was maintained at a few mbar of pressure while simultaneously being fed with a mixed gas flow of hydrogen and nitrogen ranging from 10 to 100 slh. Using in situ infrared laser absorption spectroscopy with lead salt tuneable diode lasers and external-cavity quantum cascade lasers, the temperatures and concentrations of HCN, NH3, CH4, C2H2, and CO have been monitored as a function of pressure and total gas flow. To simulate industrial treatment conditions the temperature of the sample workload in the centre of the reactor volume was kept at 773 K by varying the plasma power at the AS between 6 and 8.5 kW. The resulting spectroscopically measured temperatures in the plasma agreed well with this value. Concentrations of the various species ranged from 6 × 1013 to 1 × 1016 cm−3 with HCN being the most abundant species.