DOI: 10.5281/zenodo.17976288
title: Ratio of electron-impact ionization to OI 1356 Å dissociative excitation of O$_2$ and their cross sections

description: This dataset provides most recent measured cross sections of electron-impact ionization and OI 1356 Å dissociative excitation of O$_2$ and extrapolations as well as the ionization-to-excitation ratio for electrons with Maxwell energy distributions as collected or calculated in Duling et al. (2026) (Figure 1).

Cross Sections

The file cross_sections.txt contains measured or extrapolated cross sections for electron-impact ionization of O$_2$, OI 1356 Å dissociative excitation of O$_2$ and OI 1356 Å excitation of O as function of electron energy $W_e$ in the range 10$^1$-10$^5$ eV. Measured cross sections are linearly interpolated. For higher energies the measured cross sections are extrapolated using Bethe-Oppenheimer relations $AW_e^{-1} \ln\left(BW_e\right)$. 

The cross sections are total cross sections, meaning excitation interactions that excite to higher states than $^5S$ (1356 Å emission) but cascade to $^5S$ are included.

The ionization cross sections include ionization interactions that produce (1) O$_2^+$, (2) O$^+$ + O$_2^{++}$ and (3) O$^{++}$.

The measured cross sections are combined from the following publications:



electron-impact ionization of O$_2$: $W_e\le$1000 eV Straub et al. (1996)1000 eV $<W_e\le$20000 eV Schram et al. (1965)$W_e>$20000 eV extrapolation using the 600 eV $\le W_e\le$20000 eV data from Schram et al. (1965).

OI 1356 Å dissociative excitation of O$_2$: $W_e\le$600 eV Kanik et al. (2003)$W_e>$600 eV extrapolation using the $W_e>$100 eV data from Kanik et al. (2003).

OI 1356 Å excitation of O: 13 eV $<W_e\le$48 eV Julienne et al. (1976)


The file contains the following columns:




W_e_[eV]
electron energy in eV


ion_[cm^2]
total cross section for electron-impact ionization of O$_2$ in cm$^2$


source
source of electron-impact ionization cross section


1356_O2_[cm^2]
total cross section for OI 1356 Å dissociative excitation of O$_2$ in cm$^2$


source
source of OI 1356 Å dissociative excitation of O$_2$ cross section


1356_O_[cm^2]
cross section for OI 1356 Å excitation of O in cm$^2$


source
source of OI 1356 Å excitation of O cross section




Ionization-to-excitation ratio

The file ratio_rate_coefficients.txt contains interaction rate coefficients for electrons with Maxwell distributed energies as function of temperate $T$ in the range 1-10$^4$ eV, calculated as\begin{equation}k=\int_{0}^{10^5\mathrm{ eV}} f(v)\sigma(v)v \,\mathrm{d}v,\end{equation}where $\sigma(v)$ is the cross section of the interaction, $f(v)$ is the Maxwell speed distribution and $v=\sqrt{2W_e/m_e}$ is the speed of the electrons.

The ratio\begin{equation}\beta_{\mathrm{ion/1356}}=\frac{k_{\mathrm{ion}}}{k_{\mathrm{1356}}}\end{equation}gives the ionization-to-excitation ratio and is used in Duling et al. (2026) to constrain electron-impact ionization rates from brightness observations of OI 1356 Å emissions.

The file contains the following columns:




T_[eV]
temperature of the Maxwell distribution in eV


k_ion_[cm^3/s]
rate coefficient for electron-impact ionization of O$_2$ in cm$^3$/s


k_1356_[cm^3/s]
rate coefficient for OI 1356 Å dissociative excitation of O$_2$ in cm$^3$/s


ratio_beta
ionization-to-excitation ratio $\beta_{\mathrm{ion/1356}}$