The effect of sample readsorption on thermal desorption experiments

The influence of sample readsorption on the desorption transients measured in thermal desorption experiments is discussed. In particular, shifts in the temperature of the maximum of the rate of change of the number of sorbed atoms for first and second order desorption transients are calculated in the approximation of small (βτ/ΔW where β is the sweep rate, τ the vacuum time constant and ΔW the width (K) of the desorption transient. Evidence of significant distortion when sample readsorption is moderate is given from numerical solutions of the appropriate equation. A framework is proposed in which activation energies for desorption can be calculated in the presence of non-negligible sample readsorption.