Dependence of positron-molecule binding energies on molecular parameters.

Positron binding energies $\varepsilon_{b}$ have been measured for over 85 molecules. They have been shown to depend on global molecular parameters including the molecular polarizability $\alpha$, permanent dipole moment $\mu$, and the number of $\pi$ bonds, N$_\pi$. The relationship to the ionization potential and molecular geometry (e.g., isomers) has also been discussed. The underlying physical mechanisms for binding have been elucidated by several recent theories that go well beyond global parameter scaling. However, here we use an expanded data set [i.e., $\alpha$ ($3-30 \times 10^{-30}$ m$^3$), $\mu$ ($0-4.5$ D) and N$_{\pi}$ ($0-5$)] to show that a simple linear regression captures much of the variation of $\varepsilon_{b}$ for a wide class of molecules up to an rms error of $\sim 30$ meV. While this does not improve upon theoretical results, it can provide a useful estimate of $\varepsilon_{b}$ for molecules similar to those in the data set. The effects of other parameters, outliers in the scaling results, and limitations of this approach will be discussed.