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Atomic models specify which atomic energy levels are to be used in a SPECT3D simulation, and the degree of energy level splitting (e.g., fine structure splitting, term-split, or configuration averaging; see also Atomic Models: A Primer).
The ATBASE atomic database contains data for a very large number of atomic energy levels and transitions. Using all of the data for a given atomic element is generally not needed for a typical application, and would result in substantial inefficiencies in CPU and memory. Because different problems have different requirements in regards to the portion of the spectrum being studied, the amount of detail needed in the spectrum, and the range of ionization stages that are important, SPECT3D utilizes a modeling approach that allows users to tailor the level of detail used in the atomic physics to the requirements of their problem.
To assist the user, a number of preconfigured atomic models are distributed with the SPECT3D software package. In addition, users can created their own customized atomic models using the AtomicModelBuilder application. With the AtomicModelBuilder application, users can view and edit the energy levels selected for use in a calculation, and specify how the energy levels are bundled.
Preconfigured atomic models are supplied for:
Backlighter Imaging models include all ionization stages, but only include the ground state energy levels for each ion. These are generally appropriate for simulating images where most of the absorption is due to bound-free transitions.
Backlighter K-shell Spectroscopy models include all ionization stages, and include atomic levels with K-shell vacancies (i.e., autoionization levels) for Ne-like through He-like ions. These models are particularly well-suited for investigations involving Kα and Kβ satellite (inner-shell) absorption spectroscopy.
Emission Imaging models include all ionization stages, and configuration-averaged levels up through n = 4 and hydrogenic levels for n > 4. These are appropriate for simulating images, even when most of the emission is due to bound-bound transitions. Simulated spectra using this model are less detailed due to using configuration-averaged levels.
Emission K-shell Spectroscopy models include only ionization stages from Be-like (with 4 bound electrons) through fully ionized. The model contains very detailed atomic level structures for Li-, He-, and H-like ionization stages (including 2l2l', 2l3l', and 3l3l' autoionization levels), while only the ground states of Be-like ions are included.
Emission Visible/UV/EUV Spectroscopy models include all ionization stages, and include excited state energy levels over a broad range of ionization stages. No autoionization states are included. Term-split modeling is used for computing spectra, and configuration-averaged modeling is used in computing non-LTE atomic level populations. To produce more detailed spectra for specific ions, users should set up custom atomic models (using AtomicModelBuilder) in which fine structure splitting is used for the ions of interest.
Low Temperature Spectroscopy models include all ionization stages, but include only ground states for ionization stages beyond the lowest 4 ionization stages of the element. For the lowest 4 ionization stages, all levels are selected. Fine structure splitting is used for computing spectra, and configuration-averaged modeling is used in computing non-LTE atomic level populations. No autoionization states are included.
Preconfigured atomic models are located in the Atomic Database Library (i.e., the folder containing the atomic database). Users can specify the default location of this folder in the Preferences dialog.
Users can also build their own custom atomic models using the AtomicModelBuilder application. For information on this, see the on-line user's manual for AtomicModelBuilder.
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