Dependence of positron-molecule binding energies on molecular properties

Positron annihilation on many molecular species occurs via capture into vibrational Feshbach resonances. The study of the downshifts in the energy of these resonances from the vibrational modes in the molecule using a tunable, high-resolution positron beam provides a measure of the positron-molecule binding energy. Regression analysis on data for 30 molecules is used to identify the molecular properties that affect these binding energies. One parameterization that fits the data well involves a linear combination of the molecular dipole polarizability, the permanent dipole moment and the number of pi bonds in aromatic molecules. The predictions of this empirical model are compared with those from positron-molecule binding energy calculations. They are also tested in cases where other experimental evidence indicates that molecules do and do not bind positrons. Promising candidate molecules for further experimental and theoretical investigation are discussed.