Effect of chlorination on positron binding to hydrocarbons: experiment and theory

TL;DR

This study combines experimental measurements and theoretical calculations to investigate how chlorination affects positron binding energies in hydrocarbons, revealing significant effects and sensitivities to molecular structure.

Contribution

It provides the first comprehensive comparison of experimental and theoretical positron binding energies for chlorinated hydrocarbons, highlighting the impact of chlorine atoms.

Findings

Chlorination significantly increases positron binding energies.

Binding energies are highly sensitive to chlorine atom positions.

Good agreement between experiment and theory, except for some chlorinated compounds.

Abstract

Measured and calculated positron binding energies are presented for a range of hydrocarbons with up to six carbon atoms (viz., methane, acetylene, ethylene, ethane, propane, butane, and hexane) and their chlorinated counterparts. Both experiment and theory confirm the large effect that the chlorine atoms have on the positron binding energy and the strong sensitivity of the binding energy to the exact position of the chlorine atoms. The experimental binding energies have been obtained by measuring positron resonant annihilation using a trap-based positron beam. The calculations are performed using the previously developed model-correlation-potential method [A. R. Swann and G. F. Gribakin, J. Chem. Phys. 149, 244305 (2018)]. The overall trends are discussed with regard to the molecular polarizability, dipole moment, and geometry. Good agreement between theory and experiment is found, with the exception of the chlorinated ethylenes and chlorinated hexane. Calculations of the electron-positron annihilation rate in the bound state are also presented.