Excitation and ionization by electron impact in transition and supertransition arrays

This study investigates the ionization and excitation processes induced by electron impact between two configurations or superconfigurations. Rate coefficients are calculated for transition arrays or supertransition arrays rather than level-to-level transitions. Special attention is given to a series of oxygenlike ions relevant to inertial confinement fusion, specifically silicon, germanium, argon, and krypton. Calculations are performed over a wide temperature range, from 50 to 3000 eV. To facilitate the determination of rates at any temperature and ion charge, the computed rates are fitted with a two-dimensional Chebyshev polynomial expansion, yielding a set of coefficients for practical applications. Additionally, an extension of the Clenshaw algorithm to two dimensions, using the Chebyshev coefficients, is proposed to address numerical challenges and enhance computational efficiency.