Kinetics of Desorption. II. Cs+ and Ba+ from Rhenium

The mean desorption lifetimes (τ3) of Cs+ and Ba+ on an atomically clean rhenium surface have been measured. Under conditions of low surface coverage τ3=(1.9±0.9)×10−13exp(23 300±500T)secwas obtained for Cs+ in the temperature range 950<T<1080°K. This is in excellent agreement with the data obtained previously for the Cs+–W system. For Ba+ on rheniumτ3=(0.6±0.4)×10−13exp(54 700±2400T)secwas obtained in the temperature range 2100<T<2310°K. The Cs+–Re, like the Cs+–W bonding, can be attributed to the electrostatic image energy of a Cs+ ion on an electrically conducting surface. The Ba+–Re interaction, on the other hand, must include a large exchange force in addition to the electrostatic image force because of the unpaired valence electron remaining in the univalent barium positive ion. The presence of an adsorbed layer of residual vacuum gases decreased the Cs+–Re binding energy by 0.4 eV and increased the pre-exponential factor by two orders of magnitude. These results are almost identical with that reported previously for Cs+ desorbing from a contaminated tungsten surface.