Data on cross-sections for Stark broadening of radio recombination lines: non-perturbative all-multipole classical calculations

Abstract

The Stark broadening of hydrogen radio recombination lines (RRLs), observed from galactic H II regions, is controlled by inelastic collisions with charged particles. There is a dramatic discrepancy—up to several hundred percent—between cross-sections of inelastic electronic collisions (causing the radiative transitions between the Rydberg levels) calculated by various authors. This dramatic discrepancy in cross-sections leads to a significant discrepancy in spectral line widths of RRLs. In this paper, we address two problems: (i) whose results for the cross-sections of the radiative transitions between the Rydberg levels are the most reliable and should be recommended to astrophysicists-observers for their analysis of the measured profiles of RRLs? (ii) How can one allow for all major processes relevant to the Stark broadening of RRLs (transitions between discrete levels, ionization, charge exchange) within a single/unified theoretical approach? For this purpose, we employed calculations in frames of the classical trajectory Monte Carlo approach. We obtained the results for a broad range of velocities of the charged particles (both electrons and protons), including the region most difficult for the analytical description, where the velocities of both the incident particle and the atomic electron have the same order of magnitude. By benchmarking analytical and semi-empirical results of other authors to our calculations (which are non-perturbative and do not use the dipole approximation), we have found which one is the most accurate and should be recommended to astrophysicists-observers for their analysis of the measured profiles of RRLs.