Measurements of positron-molecule binding energies are made for molecules with large permanent dipole moments ($>2.7\mathrm{D}$), by studying vibrational-Feshbach-mediated annihilation resonances as a function of incident positron energy. The binding energies are relatively large (e.g., $\ge 90\mathrm{meV}$) 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.

• Received 27 April 2010

DOI:https://doi.org/10.1103/PhysRevLett.104.233201