Narrow resonances seen in alkali photodetachment

While making the first accurate experimental determinations of the electron affinities of alkali negative ions, a team at the Joint Institute for Laboratory Astrophysics (of the University of Colorado and the National Bureau of Standards, Boulder) has stumbled upon what appears to be by far the narrowest resonance observed in any electron–atom scattering process. Tom Patterson, Hartmut Hotop, Abe Kasdan, David Norcross and Carl Lineberger report their work with lithium, sodium, potassium, rubidium and cesium negative ions in the 4 February issue of Physical Review Letters. As well as giving the electron affinities for these ions the JILA team shows cross‐section curves for the photodetachment process that include strong resonances, as narrow as 150 microelectron volts (FWHM) in the case of rubidium. These resonances, not predicted by previously existing theoretical work, occur near photon energies corresponding to the formation of the neutral atom in its first excited $(2P)$ state. The JILA group, an unusual collaboration of theoretical and experimental specialists working on the same problems, also reports improved calculations for these scattering processes that show theoretically how the resonances arise.