Heterogeneous and homogeneous hydrogen kinetics in plasma chemistry

Abstract. A review of gas phase and surface kinetics of hydrogen radicals in excited hydrogen molecules strongly influences the mechanisms of the chemical reactions. Both homo-and heterogeneous collisional processes are analysed in that respect. As will be shown, ionizing plasmas are dominated by gas phase rovibrationai excitation phenomena. By contrast the kinetics of recombining plasmas are strongly influenced by heterogeneous elementaly processes, where they can be distinguished in a natural way. Examples of heterogeneous catalysis in plasmas, i.e. particle excitation phenomena at surfaces, are discussed

Absolute density of the argon first excited states in plasmas used for carbon deposition as determined by absorption spectroscopy Citation for published version (APA)

Absolute density of the argon first excited states in plasmas used for carbon deposition as determined by absorption spectroscopy Abstract In order to study the possible excitation transfer from argon metastables to the admixed species in an expanding cascaded arc plasma the densities of the Ar( 3p54s) states in a deposition plasma were studied with absorption spectroscopy. For a purely argon plasma the Ar(3p54s) density lies in the range 10'6-10'8 me3 at a chamber pressure of 40 Pa. The effect on the densities of the addition of moderate amounts of methane and oxygen is small. The addition of hydrogen to the argon plasma leads to a rapid disappearance of the argon 4s states. Possible explanations are a lowering of the argon ion density by dissociative recombination and the direct excitation energy transfer with the H* (n=2, 3) levels

Diagnostics of the magnetized low-pressure hydrogen plasma jet : molecular regime

Optical emission and absorption spectroscopy and double Langmuir probe diagnostics have been applied to measure the plasma parameters of an expanding magnetized hydrogen plasma jet. The rotational temperature of the excited state H2(d2¿u) has been determined by analyzing the intensity distribution of the spectral lines of the Fulcher-a system of H2. The gas temperature in the plasma, which is twice the value of the rotational temperature is equal to ¿ 520 K. Several clear indications of presence of the ‘‘hot’’ electrons have been observed in the plasma: (1) Langmuir probe measurements (Te¿1.4 eV), (2) appearance of the Fulcher-a system of H2 (excitation potential ¿E=13.87 eV), (3) low rotational temperature (T*rot¿260 K) of the excited H2(d3¿u) molecules, (4) local excitation in the plasma of Ar¿I(¿E=15.45 eV), and Ar¿II(¿E=19.68 eV) spectral lines, (5) local excitation in the plasma of He¿I(¿E=23.07 eV and ¿E=24.04 eV) spectral lines. Optical actinometry has been applied to measure the absolute density of hydrogen atoms and hydrogen dissociation degree in the plasma. The measured absolute density of hydrogen atoms are in the (1–1.4)×1020 m-3 range, and the corresponding dissociation degree of the hydrogen plasma is in the range of 8%–13%