Desorption kinetics at atmospheric pressure: Alkali metal ion emission from hot platinum surfaces

The kinetics of potassium and cesium ion desorption from platinum surfaces have been studied with field reversal technique under atmospheric condition s. Rapid electric field reversal outside the surface disturbs the surface p opulation of alkali metal atoms by retarding or accelerating desorbing ions , and the flux of ions from the surface is monitored to determine rate cons tants for desorption. Ion desorption from polycrystalline platinum surfaces in air is studied to evaluate the potential of the method for in situ high -pressure investigations. Rate constants in the range 10(-2)-10(3) s(-1) ar e obtained at surface temperatures of 820-1290 K, and activation energies ( frequency factors) of 2.49 +/- 0.06 eV (3.7 x 10(13) s(-1)) and 1.80 +/- 0. 09 eV (5.4 x 10(11) s(-1)) are determined for K+ and Cs+, respectively. The results are in excellent agreement with literature data obtained under ult rahigh vacuum conditions, which confirms that the field reversal technique can be successfully applied under pressurized conditions. The implications of the results for new experimental investigations are discussed.