The Recombination and Level Populations of Ions—I HYDROGEN AND HYDROGENIC IONS

Abstract

A description is given of the atomic processes occurring in an unbounded plasma containing ions, electrons and protons and permeated by external radiation fields. The ionization equilibrium is formulated in a matrix scheme which simplifies the definition of the effective recombination and ionization rate coefficients, namely the ‘ collisional radiative coefficients ’, and also permits the unification of statistical and mechanistic approaches to recombination. A method of numerical solution of the statistical balance equations for the collisional radiative coefficients and the level populations (including the very highly-excited levels) is given. Results are presented for hydrogen and hydrogenic ions in both graphical and numerical form. The collisional radiative recombination and ionization coefficients are given for hydrogen and hydrogenic ions over wide ranges of electron density and temperature. The influence of radiation and free particle temperature and density on the excited level populations of hydrogen is demonstrated. Tabulations of level populations are given appropriate to H I regions and to fairly dense H II regions. Simple expressions for bound-bound and bound-free Gaunt factors and for impact parameter cross-sections are given as Appendices.