Dipole enhancement of positron binding to molecules.

Measurements of positron-molecule binding energies are made for molecules with large permanent dipole moments (>2.7  D), by studying vibrational-Feshbach-mediated annihilation resonances as a function of incident positron energy. The binding energies are relatively large (e.g., ≥90  meV) as compared to those for similar sized molecules studied previously and analogous weakly bound electron-molecule (negative ion) states. Comparisons with existing theoretical predictions are discussed.