# Testing atomic collision theory with the two-photon continuum of astrophysical nebulae

## TL;DR

This paper investigates how different theories of l-changing collisions affect the two-photon continuum in astrophysical nebulae, proposing that observations could distinguish the correct atomic process model.

## Contribution

It provides an analysis of competing atomic theories for l-changing collisions and offers updated recombination coefficients and transition rates for astrophysical modeling.

## Key findings

- Two-photon continuum is strongly influenced by l-changing collisions.
- Updated recombination coefficients are provided for different theories.
- Potential for astronomical observations to test atomic collision theories.

## Abstract

Accurate rates for energy-degenerate l-changing collisions are needed to determine cosmological abundances and recombination. There are now several competing theories for the treatment of this process, and it is not possible to test these experimentally. We show that the H I two-photon continuum produced by astrophysical nebulae is strongly affected by l-changing collisions. We perform an analysis of the different underlying atomic processes and simulate the recombination and two-photon spectrum of a nebula containing H and He. We provide an extended set of effective recombination coefficients and updated l-changing 2s-2p transition rates using several competing theories. In principle, accurate astronomical observations could determine which theory is correct.