.. _physics-atomicCrossSectionIonizationPhoto: Atomic Cross-sections for Photo-ionization ========================================== Class providing photo-ionization cross sections (in cm\ :math:`^2`) for atoms of a given atomic number in a specified ionization state and electron shell, as a function of photon wavelength (in \AA). These cross sections are used in radiative transfer and :term:`IGM` ionization calculations to compute the rate at which photons are absorbed by neutral or partially-ionized gas. **Default implementation:** ``atomicCrossSectionIonizationPhotoVerner`` Methods ------- ``crossSection`` → ``double precision`` Returns the cross-section for photoionization (in units of cm\ :math:`^2`) for a given atom in a given ionization state at the specified ``wavelength`` (given in units of \AA). * ``integer , intent(in ) :: atomicNumber, ionizationState, shellNumber`` * ``double precision, intent(in ) :: wavelength`` .. _physics-atomicCrossSectionIonizationPhotoVerner: ``atomicCrossSectionIonizationPhotoVerner`` ------------------------------------------- An atomic photoionization cross section class based on (`phfit2.f `_) written by `D. A. Verner `_ (Version 2. March 25, 1996). **(Default implementation)**