Electron-Impact Excitation and Ionization of Atomic Oxygen

Abstract

We utilize the analytic atomic independent-particle model (IPM) of Green, Sellin, and Zachor to calculate generalized oscillator strengths (GOS) and total cross sections for excitation and ionization of atomic oxygen. First we average over the experimental energy levels within a multiplet to arrive at single-particle levels. Then we adjust the two parameters of the IPM potential so that it accurately characterizes the ground state and 15 lowest excited states. Using the wave functions so obtained, and assuming the Born approximation and the I S-coupling scheme, we calculate absolute GOS and cross sections for excitation to these levels, and for ionization with incident energies up to 1000 eV and secondary electron energy up to 200 eV. We obtain an analytic representation of the excitation GOS as a function of the momentum transfer. We also obtain an analytic representation of the energy differential cross section for ionization as a function of the energies of the incident and secondary electrons. Comparison is made with available experimental data and other calculations.

Infrared Spectroscopy of Supernovae

“…The lack of hydrogen lines in the spectra and the large masses of iron seen the late time spectra (Kirshner & Oke 1975, Meyerott 1980, Axelrod 1980) supports this scenario. The fusion energy released may propagate through the star as a detonation or a deflagration.…”

“…1983). Later spectra of Type la supernovae require Fe to be included in the models, with spectra a year after maximum being fitted almost entirely by transitions of Fe II and Fe III (Kirshner & Oke 1975). SN 1986G, the nearest Type la since SN 1972E, was discovered (Evans 1986) in NGC 5128 and has provided us with unique early-time infrared spectra of such an event (Frogel et dl.…”

“…Although a more detailed calculation should include all species present in the ejecta it should be pointed out that the results of this Monte-Carlo calculation, in the high ionisation limit, agree with the semi-analytical calculations of Axelrod (1980) for iron. The excitation cross-sections for O I are from Kazaks et al (1972), Sawada & Ganas (1973), Thomas & Nesbet (1975) and Smith (1976). The fact that we ignore excitations of other ionisation stages does not affect our results adversely as we shall see that excitations to not form a major deposition path for the primary electrons for the conditions observed to be present in the supernova.…”

Electron impact excitation cross sections for O II

“…The general formulas which are used to compute the GOS are based upon the first Born approximation and the Russell-Saunders LS coupling scheme, and may be found in a previous paper [5]. The following notation is introduced for use in subsequent discussions.…”

New analytical independent-particle model potential for atoms

“…In 1969 Green et al [18] presented a very successful analytical independent-particle model (IPM) potential with a simple analytical form. It has been widely used for the calculation of electron-atom and atom-ion scattering [19,20], electron impact excitation and ionization [21][22][23], oscillator strengths [21], antiproton-atomic collisions [24], and electron-capture processed [25,26].…”