TDS spectra analysis

Abstract

Methods of TDS spectra analysis start usually from the Polanyi-Wigner desorption rate equation. The Redhead approximative solution of the equation can be rearranged into a reduced form in which it serves as an analytical expression for the desorption rate versus time or temperature. Fitting the analytical form to an experimental curve we can confirm or deny the invariability of kinetic parameters — a desorption energy E d and a preexponential factor ν l — and determine their values. If the parameters depend on surface coverage Θ the application of the reduced form allows us to determine their values at Θ→0 and Θ→ Θ 0 and estimate the dependence E d( Θ), ν(Θ) from a single TDS spectrum. The method proposed in this paper is valid for the first-order kinetics of desorption; for the estimation mentioned above an assumption is made that desorption sites are identical and that E d as well as ν l changes with Θ monotonously.