# Electron capture and ionization cross-section calculations for proton collisions from methane and the DNA and RNA nucleobases

## TL;DR

This paper introduces a new geometrical pixel counting method for calculating ionization and capture cross sections in proton collisions with methane and DNA/RNA nucleobases, showing improved accuracy at low energies.

## Contribution

The paper presents the independent-atom-model pixel counting method, a novel approach that accounts for atomic overlap, providing more accurate cross-section calculations at low energies.

## Key findings

- Pixel counting method agrees with experimental data at low energies.
- It predicts smaller cross sections for nucleobases than previous models.
- High-energy results are consistent across different methods.

## Abstract

Net ionization and net capture cross-section calculations are presented for proton collisions from methane molecules and the DNA/RNA nucleobases adenine, cytosine, guanine, thymine, and uracil. We use the recently introduced independent-atom-model pixel counting method to calculate these cross sections in the 10 keV to 10 MeV impact energy range and compare them with results obtained from the simpler additivity rule, a previously used complete-neglect-of-differential-overlap method, and with experimental data and previous calculations where available. It is found that all theoretical results agree reasonably well at high energies, but deviate significantly in the low-to-intermediate energy range. In particular, the pixel counting method which takes the geometrical overlap of atomic cross sections into account is the only calculation that is able to describe the measurements for capture in proton-methane collisions down to 10 keV impact energy. For the nucleobases it also yields a significantly smaller cross section in this region than the other models. New measurements are urgently required to test this prediction.