Positron binding to chlorinated hydrocarbons: experiment and theory.

Measurement of the low-energy positron annihilation on molecules 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. The calculations are performed using the model-correlation-potential method.\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 experiments. 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.