Measurement and modeling of positron binding to chlorinated hydrocarbons.

Positron annihilation on molecules at low energies is dominated by vibrational Feshbach resonances. The downshift of the resonances relative to the known molecular vibrations provides a measure of the positron-molecule binding energy, $\epsilon_b$. Measured and calculated positron binding energies are presented for a range of hydrocarbons and their chlorine-substituted counterparts.\footnote{\small A. R. Swann, et al., arXiv:2104.05338 (2021).} The calculations are performed using a model correlation potential.\footnote{\small A. R. Swann and G. F. Gribakin, J. Chem. Phys. 149, 244305 (2018).}$^{,}$\footnote{\small A. R. Swann and G. F. Gribakin, Phys. Rev. Lett 123, 113402 (2019)} Generally good agreement is found between the model predictions and the experimental measurements. Both experiment and theory demonstrate the large effect that the chlorine atoms have on $\epsilon_b$ and the strong sensitivity of $\epsilon_b$ to the position of the Cl atoms. Overall trends with molecular polarizability, dipole moment, and geometry are discussed. Calculated wavefunctions and the electron-positron annihilation rates in the bound state will also be discussed.