Rydberg states of cesium in the flux from surfaces at high temperatures

Abstract

Diffusion of cesium through an Ir foil at high temperature is used to give a flux of desorbing atoms and/or ions, which is not in equilibrium at the surface temperature. The desorbing flux is studied with electrostatic fields in a grid-collector combination, to determine the charge states and the interaction of the different states with an electric field and with a surface. At low Cs flux densities to the back of the foil, the desorbed flux contains positive ions and ordinary neutrals. At large flux densities from the source, however, both neutral Rydberg states and negative ions in the form of multiply-excited states of cesium are found in the flux. The negative ion states do not dissociate (detach) readily in such weak external electric fields where the neutral Rydberg state atoms ionize. Instead, they can emit two of their outer electrons in contact with the collector surface, thus giving positive collector currents when the field accelerates the electrons away from the collector. The large flux of such states indicates that the electron affinity is large for Rydberg state atoms. The origin of the excited states leaving the hot Ir surface is discussed. It appears to be related to the close coincidence of the desorbing ionic state and the Rydberg state at low work function.