High resolution studies of electron excitation II. The 33D, 43D and 41D states of helium: features in the <i>n</i> = 4 excitation functions

Abstract

Abstract We present excitation functions of the 41D, 33D and 43D states of helium for energies within about 1 eV of threshold. We find a series of broad features and some sharp features and discuss their interpretation. The broad features appear to be shape resonances and to occur, at least in part, as a result of cascade from F states. We suggest that the prominent features in the 4S excitation functions are due to Feshbach resonances having configurations 1s 5s2 and 1s 5p2. We interpret a very small feature at the threshold of both 4D functions as a 1s 4d2 Feshbach resonance.