# H-, He-like recombination spectra III: $n$-changing collisions in highly-excited Rydberg states and their impact on the radio, IR and optical recombination lines

## TL;DR

This paper investigates the impact of uncertainties in $n$-changing collisional rates on the prediction of radio, IR, and optical recombination lines in gaseous nebulae, showing errors are generally below 5% but can reach 20% in maser-affected cases.

## Contribution

It provides a detailed analysis of how different datasets of collisional rates affect the modeling of recombination spectra and quantifies the resulting errors in various astrophysical environments.

## Key findings

- Uncertainties in collisional rates cause less than 5% error in most cases.
- Errors can reach up to 20% in maser amplification scenarios.
- Simulations of AGN BLRs and Orion Nebula support these conclusions.

## Abstract

At intermediate to high densities, electron (de-)excitation collisions are the dominant process for populating or depopulating high Rydberg states. In particular, the accurate knowledge of the energy changing ($n$-changing) collisional rates is determinant for predicting the radio recombination spectra of gaseous nebula. The different datasets present in the literature come either from impact parameter calculations or semi-empirical fits and the rate coefficients agree within a factor of two. We show in this paper that these uncertainties cause errors lower than 5% in the emission of radio recombination lines (RRL) of most ionized plasmas of typical nebulae. However, in special circumstances where the transitions between Rydberg levels are amplified by maser effects, the errors can increase up to 20%. We present simulations of the optical depth and H$n\alpha$ line emission of Active Galactic Nuclei (AGN) Broad Line Regions (BLRs) and the Orion Nebula Blister to showcase our findings.