Near-threshold electron impact excitation of Kr

Absolute differential cross sections and energy dependences for excitation of each of the four 4p 5 5s states of Kr are measured within the first 4 eV of threshold using a crossed-beam electron impact spectrometer which has been modified to achieve controlled transmission of low-energy (100 meV-4 eV) scattered electrons. These are the first absolute measurements of near threshold to be reported for any heavy noble gas. The observed large differences in the relative magnitudes of the cross sections are interpreted in terms of the angular momenta of the Kr + ion core (4p 5 ) and the entire electron configuration. A resonance is found to be most prominent in the excitation functions of states having the same core angular momentum as that of resonance itself, indicating that the rearrangement involved in the decay of a temporary negative ion generally involves only the outer electrons.