Threshold photoelectron spectroscopy with velocity focusing: an ideal match for coincidence studies

Velocity focusing of low energy electrons has been used to collect threshold photoelectron spectra with a continuous tunable vacuum UV light source. Velocity focusing permits focusing the photoionization image from 5 mm x 8 mm to 1 mm x 1 mm, and thus to collect threshold electrons (less than 10 meV) with a collection efficiency close to 50%. The overall resolution for Xe+ of 13 meV is limited primarily by the 12 meV band pass of the photon monochromator: The collection efficiency for energetic electrons of 1 eV is reduced 0.07%. This method of detecting threshold electrons has improved the resolution by a factor of 4 and increased the signal by a factor of 10. It is an ideal approach for photoelectron photoion coincidence (PEPICO) studies because it permits the collection of electrons and ions with relatively high electric fields of 20 V/cm, which are necessary to have narrow time of flight peaks for the coincident ion signals.