We study temperature programmed desorption of sodium and chlorine from an electron irradiated sodium chloride (100) surface. In this experiment, the sodium chloride crystal is irradiated with 500 eV electrons. After the electron beam is turned off, the crystal is heated and desorption of the alkali atoms is observed. This delayed desorption of sodium is analyzed using fractional order desorption equations. The results clearly show that the desorption is not a first order process. The data are interpreted in terms of a thick layer of sodium forming on the surface.