find each other and recombine into the desorption product. An example of second order desorption, , is when two hydrogen atoms on the surface desorb and form a gaseous molecule. There is also zeroth order desorption which commonly occurs on thick molecular layers, in this case the desorption rate does not depend on the particle concentration. In the case of zeroth order, , the desorption will continue to increase with temperature until a sudden drop once all the molecules have been desorbed. In a typical thermal desorption experiment, one would often assume a constant heating of the sample, and so temperature will increase linearly with time. The rate of heating can be represented by Therefore, the temperature can be represented by: where is the starting time and is the initial temperature. At the "desorption temperature", there is sufficient thermal energy for the molecules to escape the surface. One can use the thermal desorption as a technique to investigate the binding energy of a metal. There are several different procedures for performing analysis of thermal desorption. For example, Redhead's peak maximum method is one of the ways to determine the activation energy in desorption experiments. For first order desorption, the activation energy is estimated from the temperature (Tp) at which the desorption rate is a maximum. Using the equation for rate of desorption (Polyani Winer equation), one can find Tp, and Redhead shows that the relationship between Tp and E can be approximated to be linear, given that the ratio of the rate constant to the heating rate is within the range 10 – 10. By varying the heating rate, and then plotting a graph of against , one can find the activation energy using the following equation: This method is straightforward, routinely applied and can give a value for activation energy within an error of 30%. However a drawback of this method, is that the rate constant in the Polanyi-Wigner equation and the activation energy are assumed to be independent of the surface coverage. Due to improvement in computational power, there are now several ways to perform thermal desorption analysis without assuming independence of the rate constant and activation energy. For example, the "complete analysis" method uses a family of desorption curves for several different surface coverages and integrates to obtain coverage as a function of temperature. Next, the desorption rate for a particular coverage is determined from each curve