Diagnosis Of Atomic Hydrogen And Metastable Molecular Hydrogen Anion In Hydrogen Plasmas

Atomic hydrogen density in dielectric barrier discharge hydrogen plasmas has been determined for the first time via threshold ionization-molecular beam mass spectrc,metry (TI-MBMS) and actinometric optical emission spectrometry (AOES), respectively. Strong metastable H₂ and D₂ ions have been observed from low-pressure dielectric barrier discharge hydrogen and deuterium plasmas via molecular beam mass spectrometry and their possible formation mechanisms have been investigated. The main results presented in the dissertation have been summarized as followings:1. Atomic hydrogen density near the grounded electrode in dielectric barrier discharge hydrogen plasmas has been experimentally determined for the first time via TI-MBMS. A method has been proposed and performed for the first time to determine the total discrimination factor formed in the processes of beam formation and mass spectrometry measurement for the determination of atomic hydrogen density. It is shown that at certain discharge conditions (28 kV of peak-to-peak voltage, a.c. frequency of 24 kHz) the dissociation fraction of H₂ near the grounded electrode is decreased from 0.83% to 0.14% as the gas pressure increases from 2.0×133 Pa to 14.0×133 Pa. The gas temperature near the grounded electrode has been investigated experimentally and it is shown that the rise in gas temperature caused by the discharge can be ignored, so above H₂ dissociation fractions correspond to atomic hydrogen densities around 1.0-3.0×10¹⁵ atoms cm^-3.2. The dissociation fractions of H₂ and the atomic hydrogen density in the discharge volume of dielectric barrier discharge hydrogen plasmas has been experimentally determined via AOES using Ar as the actinometer. It is shown that at certain discharge condit.ions (28 kV of peak-to-peak voltage, a. c. frequency of 24 kHz) the dissociation fraction of H₂ in the plasma volume is decreased from 5.2% to 0.1% as the gas pressure increases from 2.0×133 Pa to 38.0×133 Pa. And if the rise in gas temperature also can be neglected, the corresponding atomic hydrogen densities are around 2.2～6.6×10¹⁵ atoms cm^-3.3. Strong and reliable mass signals of H₂^- and D₂^- ions with long lifetime have been experimentally observed from low-pressure dielectric barrier discharge hydrogen and deuterium plasmas via molecular beam mass spectrometry. The observed H₂^-/H^- and D₂^-/D^- ratios (～0.35-0.4) are over 5 orders of magnitude higher than those observed via other techniques. The kinetic energy of H₂^- and D₂^- ions sampled from the plasmas was determined to be widely distributed, from a few eV to＞100 eV, and their lifetime greater than～40μs for H₂^- ions and～55μs for D₂^- ions can be extracted from the velocity of those anions with low kinetic energy.4. The rovibrational distribution of H₂ in the electronic ground state has been determined in low-pressure H₂ plasmas where the strong mass signals of H₂^- ions are observed via TI-MBMS and OES. The highest rovibrational excitation states of H₂ in the electronic ground state has been determined to be about J=0, v=5 or J=19, v=0 via TI-MBMS. Using OES, the vibrational temperature and rotational temperature of the electronic ground state has been extracted to be 2700 K and 400 K, respectively. The possible formation mechanisms of H₂^- ions with further high J, required by the current high-rotation model, have been proposed and discussed.