G. N. Haddad

Total and partial photoionization cross-sections of O2 from 100 to 800 Å

Abstract The branching ratios and absolute values of the total and partial photoionization cross-sections for producing O 2 + in its various electronic states are given as a function of wavelength in the range 100–800 A. Cross-sections for dissociative ionization are given based on the premise that some of the bound ionic states predissociate. Photoelectron spectroscopy and absorption techniques utilizing a double ionization chamber were used to obtain the data.

Ionization yields, total absorption, and dissociative photoionization cross sections of CH4 from 110 to 950 Å

Absolute absorption and photoionization cross sections of methane have been measured with an accuracy of about 2% or 3% over most of the wavelength range from 950 to 110 A. Also, dissociative photoionization cross sections were measured for the production of CH+4 , CH+3 , CH+2 , CH+, and C+ from their respective thresholds to 159 A, and for H+ and H+2 measurements were made down to 240 A. Fragmentation was observed at all excited ionic states of CH4.

Total and partial photoionization cross sections of N2 from threshold to 100 AA

The total photoionization cross section of N2 has been obtained from the ionization threshold to 100 AA with an accuracy of +or-3%. In addition, partial photoionization cross sections for transitions into the x2 Sigma g+, A2 Pi u and B2 Sigma u+ electronic states have been measured using the technique of photoelectron spectroscopy over the wavelength range from 745 to 304 AA. Transitions to higher electronic states are also observed at 304 AA.

Total absorption and photoionization cross sections of water vapor between 100 and 1000 A

Total absorption and photoionization cross sections of water vapor have been measured between 100 and 1000 A with an accuracy of ±3%. Recent calculations are shown to be in reasonable agreement with the present data.

Absolute photon-flux measurements in the vacuum ultraviolet

Absolute photon-flux measurements in the vacuum ultraviolet have been extended to short wavelengths by use of rare-gas ionization chambers. The technique involves the measurement of the ion current as a function of the gas pressure in the ion chamber. The true value of the ion current, and hence the absolute photon flux, is obtained by extrapolating the ion current to zero gas pressure. Examples are given at 162 and 266 A. The short-wavelength limit is determined only by the sensitivity of the current-measuring apparatus and by our present knowledge of the photoionization processes that occur in the rare gases.

Total photoabsorption cross sections of H 2 from 18 to 113 eV

The total photoabsorption cross section of H2 has been measured between 18 and 113 eV with an accuracy of ±2 to ±3%. The published data at higher energies are reviewed, and recommended cross sections are tabulated from 18 to 300 eV.

Absorption and dissociative photoionization cross sections of NH3 from 80 to 1120 Å

The total absorption, photoionization, and dissociative photoionization cross sections of ammonia have been measured from 80 to 1120 A. All possible fragment ions have been observed including doubly ionized ammonia. The absolute ionization efficiencies have also been measured in this spectral range. The appearance potentials of the fragment ions have been measured and are compared with the calculated appearance potentials derived from published heats of formation and ionization potentials of the fragments.

Double ionization of CO2 by photon impact

Abstract Double ionization of CO2 has been observed by photon impact from the double ionization threshold at 36.2 eV (342 A) to 110 eV (133 A). The ratio of doubly to singly charged ions shows a linear rise with photon energy for approximately 15 eV above the threshold and reaches a constant value of about 2% between 67 and 110 eV.

Average Energy Loss per Ion Pair Formation by Photon and Electron Impact on Xenon between Threshold and 90 eV

The W value, defined as the average energy required to form an ion pair, has been measured for xenon for bombarding electrons in the energy range 0 to 50 eV and for photons of energy between 12 and 90 eV. The W values varied between 24 and 50 eV per ion pair for the incident electrons and between 12 and 32 eV per ion pair for the incident photons.