Thermal S${\mathrm{F}}_6$ molecules have been observed to decompose and desorb as various atomic and molecular negative ions upon impact with room-temperature alkali-metal surfaces. Many of the negative ions observed have electron affinities which are less than the alkali-metal work function; hence the mechanism for ion formation and desorption is complex. A simple model is proposed to account for some of the observations.

• Received 17 February 1988

DOI:https://doi.org/10.1103/PhysRevLett.61.1194