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Photoionization cross sections for all levels belonging to the configurations of atoms and ions of aluminum, silicon, and argon have been calculated using Hartree-Fock bound-electron wave functions and close-coupling approximation free-electron wave functions. The results are presented in the form of a computationally convenient interpolation formula and should find wide astrophysical application.
The absorption coefficients of 1.15- and 3.39-micrometer radiation for a homogeneous H-He plasma have been measured in a temperature and electron density range where the major absorption mechanisms are electron-ion inverse bremsstrahlung and neutral-atom photoionization. Measurements were made behind both the incident and reflected shock waves in a driven tube by recording the laser intensity transmitted along the tube diameter as a function of time. The measured values compare well with those obtained from theoretical calculations for a gas in thermodynamic equilibrium.
Approximate values for the threshold energies, threshold cross sections, and energy dependence of the cross sections for K-shell photoionization are tabulated for H, He, C, N, O, Ne, Mg, Si, and S in all stages of ionization. The approximation of these data is based on the assumptions that the threshold energy is a simple function of the nuclear charge and the number of electrons present in the atom, and that the threshold values and energy dependence of the cross sections are determined only by the threshold energy.
Simplified photoionization calculations, considering quasar emission lines with ultraviolet rest-wavelengths, can be made including only hydrogen, helium, and carbon ions. With plausible assumptions about the helium abundance and ionizing spectral slope, estimates of the (radiation/gas) pressure ratio and carbon abundance are possible. Proportionality relations, showing the dependences of line ratios upon assumed parameters, may be useful in considering differences between individual spectra.
Description of a method for calculating the photoionization cross section of magnesium, using the technique of configuration reaction in the continuum. The two series of levels which give rise to autoionization near the threshold are explicitly included in the calculation. The described method is a logical extension of the basic technique developed by Atlick and Moore (1966) for similar calculations in application to helium.
The probability of radiation producing ions in specific electronic and vibrational levels was documented. For example, when a narrow band-pass of solar ionizing photons is incident on an atmospheric species it is now possible to describe, accurately, how the radiant energy is shared among the various electronic states of the ions produced. The molecules studied were N2, CO, and CO2. These molecules were photoionized by radiation between 53 and 75 nm. The effects of autoionization are discussed and continuum vibrational intensities are tabulated and compared with theoretical Franck-Condon factors where available. The branching ratios and partial cross sections for ionization into various electronic states are tabulated.
Measurements of the absolute photoionization cross section from the 6s5d 3D metastable level of barium are presented. The 3D levels were selectively populated with a high-power tuneable dye laser. The number density was determined by observing the resulting depopulation of the ground state when pumping occurred.
The paper reports on experimental vibrational intensity distributions for continuum photoionization of oxygen using both 584 and 304 A helium lines. A cylindrical mirror energy analyzer with known transmission properties was used to record photoelectron spectra at a resolution of 45 meV with dispersed He radiation. At each wavelength the vibrational intensity distribution were corrected for the transmission of the analyzer and normalized to 100 at the strongest level. A table lists the results with calculated Franck-Condon factors.
A detailed theoretical calculation is carried out for the photoionization of lithium at low energies within the framework of Brueckner-Goldstone perturbational approach. In this calculation extensive use is made of the recently developed multiple-basis-set technique. Through this technique all second-order perturbation terms, plus a number of important classes of terms to infinite order, have been taken into account. Analysis of the results enables one to resolve the discrepancies between two previous works on this subject. The detailed calculation also serves as a test on the convergence of the many-body perturbation-expansion approach.
The use of the Random Phase Approximation with Exchange (RPAE) for calculating partial and total photoionization cross sections and photoelectron angular distributions for open shell atoms is examined for atomic chlorine. Whereas the RPAE corrections in argon (Z=18) are large, it is found that those in chlorine (Z=17) are much smaller due to geometric factors. Hartree-Fock calculations with and without core relaxation are also presented. Sizable deviations from the close coupling results of Conneely are also found.
The photoionization of lithium from threshold to 50 eV above threshold is calculated using the method of polarized orbitals. The method is applied in as orthodox a manner as possible; this means that total wave functions are constructed as by Temkin and Lamkin (1961) using only the static dipole part of the perturbation of core electrons by the outer part of the external electron. According to other previously given prescriptions, both initial (bound) and final (continuum) wave functions are so polarized, only the length form of the matrix is calculated, and bilinear terms from the polarization contributions are retained (although their effect in this calculation is small). The results themselves are essentially identical to those of a recent diagrammatic calculation of Chang and Poe (1975) (in the region below 5 eV where thay have calculated), and as such they differ in certain significant components from exchange-adiabatic and extended-polarization results of Matese and LaBahn (1969) (although their overall result is similar). The s- and p-wave e-Li(+) phase shifts, which are derived as by-products of this calculation, are also presented and compared with other phase-shift calculations.
The absorption spectrum of Al I has been studied for the wavelength range 1160 to 2000 A by the flash pyrolysis technique. Wavelengths and derived energy levels are reported for 70 new lines converging on the 3s3p(3)P(0) limits of Al II. The autoionization parameters of the 3p(2)P(0)-3p(2)(2)S doublet have been measured. Good agreement is obtained with the experiment of Kohl and Parkinson and the recent calculation of Le Dourneuf et al. The relative photoionization cross section has been measured in the wavelength region 1200 A to 2000 A.
The formation of the ethylene oxide molecular ion and its subsequent ion-molecule reactions leading to the products C2H5O(+) and C3H5O(+) have been studied using time-resolved photoionization mass spectroscopy, ion cyclotron resonance spectroscopy, and photoelectron spectroscopy. An examination of the effects of internal energy on reactivity shows that the ratio of C3H5O(+) to C2H5O(+) increases by an order of magnitude with a single quantum of vibrational energy. The formation of (C2H4O/+/)-asterisk in a collision-induced isomerization is found which yields a ring-opened structure by C-C bond cleavage. The relaxed ring-opened C2H4O(+) ion reacts with neutral ethylene oxide by CH2(+) transfer to yield an intermediate product ion C3H6O(+) which gives C3H5O(+) by loss of H.
The charge transfer reactions: Xe(+) + O2 yields O2(+) + Xe and O2(+) + Xe yields Xe(+) + O2 were studied using photoionization mass spectroscopy. It is shown that the reaction of Xe(+)(2P-3/2) ions with O2 molecules is much more efficient than the reaction of Xe(+)(2P-1/2) ions with O2 molecules. The charge transfer reaction of O2(+) ions with Xe atoms was detected for O2(+) ions in the a 4Pi-u state.
Nitric oxide has been measured in situ between 38.4 and 29.8 km by a new technique, photoionization mass spectrometry. Data indicate a peak mixing ratio of 5.7 plus or minus 0.35 ppbv at 37.5 km and only 0.2 plus or minus 0.2 ppbv at 32.8 km with a sharp gradient in concentration between 33 and 34 km. Simultaneous in-situ measurements of the ozone concentration show no significant feature at that altitude. The rapid decrease in mixing ratio is not predicted by current theory.
Vibrational intensity distributions obtained with many discrete emission lines are presented for all major electronic states of O2(+), N2(+) and CO(+) subjected to photoionization. The vibrational distributions are reported as a function of wavelength between 745 and 304 A. The data, provided by photoelectron spectroscopy with an electron energy analyzer of known luminosity, appear to be consistent with calculated Franck-Condon Factors. Evidence for autoionization in the data is also discussed.
The absolute cross section for photoionization of atomic oxygen from the 2p4 3P ground state of O(0) to the 2p3 4S ground state of O(+) has been measured at five narrow wavelength intervals between 89.8 and 76.2 nm. The cross section near the 2p3 4S threshold is 4.5 Mb + or - 7%. Recent calculations by Taylor and Burke (1976) and by Pradhan and Saraph (1977) are in reasonable agreement with this work. The dipole-length results of Taylor and Burke (4.1 Mb) are in better agreement with the experiment than their dipole-velocity results (3.2 Mb).
Detailed time-correlated gain, fluorescence, and laser energy measurements were used to obtain quantitative data on energy extraction efficiencies for a photoionization-stabilized self-sustained XeF laser. A current pulse of 25 ns full width at half-maximum produced an 80-cu-cm XeF plasma in NF3:Xe:He gas mixtures with a maximum output energy of 80 mJ. The results show that the maximum small-signal gain and the maximum specific output energy is proportional to the NF3 content of the gas mixture. This suggests that there is an optimum fractional utilization of the NF3 molecules in the discharge. Under high-gain conditions, 30-40% of the energy stored in XeF(asterisk) can be extracted in a gain-switched pulse. The output energy represents less than 1% of the input energy.