We studied dissociation reactions of electron impact on water vapor for several fragment species at optical and near ultraviolet wavelengths (200 -850 nm). The resulting spectrum is dominated by the Hydrogen Balmer series, by the OH (A 2 Σ + -X 2 Π) band, and by the emission of ionic H2O + (A 2 A1 -X 2 B1) and OH + (A 3 Π -X 3 Σ -) band systems. Emission cross sections and reaction channel thresholds were determined for energies between 5 -100 eV.We find that electron impact dissociation of H2O results in an emission spectrum of the OH (A 2 Σ + -X 2 Π) band that is distinctly different than the emission spectra from other excitation mechanisms seen in planetary astronomy. We attribute the change to a strongly non-thermal population of rotational states seen in planetary astronomy. This difference can be utilized for remote probing of the contribution of different physical reactions in astrophysical environments.
In this work, we present an experimental study of dissociative excitation of CH 4 utilizing a crossed electron molecular beam experiment. Methane was excited by nearly monochromatic electrons generated by a trochoidal electron monochromator. The dissociative products were identified on the basis of the emission spectra in the ultraviolet-visible (UV/VIS) spectral range. The excitation functions were recorded as the function of the electron energy for different emission bands of the fragments (Balmer series for H: n = 3,4 . . . 9→2, and moreover, CH: A 2 →X 2 , CH: B S 0 ). From the experimental data we have determined the threshold energies for excitation of particular fragments. Present experimental results indicate that the threshold energies for some dissociative excitation channels could be lower by ∼1-2 eV in comparison to earlier studies and indicate that different dissociative processes may be operative at the threshold than assumed in the former studies.
We present the design, construction, and first spectra of a step-scan Michelson Fourier-transform spectrometer for optical emission spectroscopy in the UV–VIS spectral range. The mirror motion mechanism is based on a long-travel piezo-based linear translation stage with built-in position feedback. The step-scan arrangement allows for signal integration, making the instrument suitable for measurements of less intensive radiation sources and for the photon-counting technique. The spectrometer consists of two coupled Michelson interferometers, one for the spectrometer itself and the other to provide positional reference for the mirror stepping mechanism using interference fringes of a stabilized 635 nm laser diode. Using interpolation of the laser interferogram and taking advantage of the translation stage precision in linear-piezo mode, the mechanism is capable of performing 79 nm steps, which puts the Nyquist wavelength at ∼320 nm. The spectrometer was tested by measuring the spectra of HgAr cold-cathode fluorescent lamp and electron-induced fluorescence of ambient air. Two different detectors were used, an amplified photodiode detector and a photomultiplier tube module in photon counting mode. The highest achieved experimental spectral resolving power was ∼4000 using 1 mm of total mirror travel and the highest achieved noise-free dynamic range was 103. Test results show that the instrument is suitable for use with moderate-to-low intensity signal sources such as small gas discharges and spectroscopic measurements at astronomical telescopes.
This paper contains results of experimental studies of the direct current breakdown voltage curves and voltampere characteristics of discharges generated in a system consisting of two plane-parallel tungsten and molybdenum electrodes at separations from 100 μm to 1 μm. The measurements were performed in the pressure range from 22.5 Torr to 738 Torr. The results are presented in the form of Paschen curves. Based on the measured breakdown voltage curves, the effective yields have been estimated in the case of different cathode materials. Differences between them are attributed to the influence of the work function of the cathode material on the current-voltage characteristics due to field emission effect in small gaps and high pressures. At low-pressures, however, vaporation of impurities from the electrodes material becomes significant. The present paper delivers new data on DC breakdown under these experimental conditions and conditions on the validity of the Paschen law in helium and provides better insight into the role of the field emission and the electrode materials on the breakdown voltage.
We report results of an experimental study focused on the fluorescence of H 2 initiated by the impact of quasimonochromatic electrons. The emission spectra of H 2 molecules at electron energies of 25 eV, 50 eV and 100 eV have been measured in the spectral range of 320-670 nm. The emission spectrum is dominated by Balmer emission lines, Fulcher α, β, γ and δ bands and different singlet transitions of H 2 . In addition to the atomic lines and molecular bands, the presence ofu continuum radiation is present in the whole studied range. We have determined the emission cross sections (ECS) for particular processes leading to the emission of the Balmer (n = 3, 4, 5, 6, 7, 8 → 2) lines and for selected bands of the Fulcher α system of H 2 (d 3 Π u → a 3 Σ + g ) as a function of electron energy in the range 5-100 eV. Emission cross sections for the Balmer lines (n = 6, 7, 8 → 2) and Fulcher α (1, 0), (1, 1), (2, 2), (3, 3) bands were measured for the first time.
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