A simple parametrization of thermal desorption spectra: Y-factor

The parameter Y, the ratio between the full width at half maximum (FWHM) and the temperature at peak maximum (T_p), may be easily obtained from thermal desorption (TD) spectra. In this paper we exploit the functional dependences of Y on the coverage θ, the adsorption energy E(θ), and the pre-exponential factor v(θ) using computer simulations, and demonstrate their usefullness for a quick evaluation of TD spectra. (1) Since Y is independent of E as well as of the applied heating rate it may serve for comparison of spectra from different sources. (2) For a fixed value of v, Y(θ) is a smooth function if E(θ) = E₀(1 + bθ) (Bragg-Williams approximation), which makes it possible to extract b values from the Y/b relationship. (3) If both E and v are constant the simple Y/v correlation yields v values. This relationship may be used even in the case when both kinetic parameters are coverage dependent, but only in the very low coverage regime. (4) Any deviation from the trends of the Y(θ) dependences simulated for various values of b indicates that either the Bragg-Williams approximation is not justified or that both E and v are coverage dependent.