Thermal desorption of gases

Abstract Methods for determining the activation energy, rate constant and order of reaction from “flash-filament” desorption experiments are examined. Two heating schedules are considered: (a) a linear variation of sample temperature with time (T = T0+st), and (b) a reciprocal temperature variation ( 1 T = 1 T 0 −αt) . The activation energy of desorption is estimated from the temperature (Tp) at which the desorption rate is a maximum (for first-order reactions) and from the change of Tp with surface coverage (for second-order reactions). The order of the reaction is determined from the shape of the desorption rate versus time curve, or the variation of Tp with coverage. Applications of these methods to experiments on chemisorption and the desorption of ionically trapped gases are discussed. The effect of finite pumping speed in the system is analysed and the necessary corrections derived.