On the Continuous Absorption, Photoionization, and Fluorescence of H2O, NH3, CH4, C2H2, C2H4, and C2H6 in the 600-to-1000-Å Region

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Abstract
The hydrogen‐containing molecules H2O, NH3, CH4, C2H2, C2H4, and C2H6 have strong continuous absorption spectra in the 12 to 21 eV (600‐to‐1000‐Å) region. Photoionization and absorption coefficients and cross sections have been computed from absorption and ionization spectra using the Hopfield He continuum as a continuous background‐radiation source. A parallel plate combination absorption and ionization chamber was used behind the exit slit of a Seya scanning vacuum monochromator arranged for 0.5 Å bandwidth. Data were obtained with a windowless system using rare‐gas calibration to measure the absolute photon flux from which photoionization efficiencies were determined. In general, the cross sections increased with increasing number of hydrogen atoms, and for the process corresponding to electron loss by photoionization, the cross section was found to be proportional to the number of bonding electrons, varying from 17.5 Mb for H2O to over 76 Mb for C2H6 (1 Mb=10—18 cm2). Inflections in the cross‐section curves indicate processes other than simple electron loss by photoionization. Preliminary results of the fluorescence from these gases indicate that NH3, CH4, and C2H2 show measurable fluorescence. Maxima in the relative fluorescence yield curves are shown to be correlated with minima in the ionization efficiency curves, suggesting that the long‐wavelength photon emitted may be associated with ion removal, either by a molecular recombination process or by reaction leading to molecular products.

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