Delayed emission in photon stimulated desorption of alkali halides

Photon stimulated desorption of KI has been measured at several temperatures between 300 K and 485 K using photons in the energy region around the fundamental absorption threshold of KI. The yield spectra vs photon energy of the emission of potassium and iodine atoms are very similar to each other and show a weak structure near threshold, in correspondence of the main exciton absorption peak, followed by a smooth exponential increase, unrelated with the higher energy absorption features or KI. The time dependence of the desorption signal of potassium atoms, measured after turning either on or off the radiation beam, shows the existence of two simultaneous processes with completely different time constants; a 'fast' process with a time constant shorter than our time resolution of 0.5 s, and a 'slow' process with a time constant of several second.