Elastic and inelastic scattering of positrons by atoms and molecules are studied experimentally in a new range of positron energies, using a novel technique involving a magnetized beam of cold positrons. Differential cross-section measurements are presented for Ar and Kr at energies from 0.4 to 2.0 eV, and they compare well with theoretical predictions. The first low-energy measurements of the vibrational excitation of molecules by positrons is presented (i.e., ${\mathrm{CF}}_4$ at energies from 0.2 to 1 eV), and comparison with electron scattering data is discussed.

• Received 26 January 1999

DOI:https://doi.org/10.1103/PhysRevLett.82.5032