PHOTOINDUCED PROCESSES ON ALKALI COVERED SURFACES - NO DESORPTION FROM K CR2O3(0001)/

We have studied the ultraviolet laser induced desorption of NO/Cr2O3(0 001), K/Cr2O3(0001) and the coadsorbate system NO/K/Cr2O3(0001) using resonance enhanced multiphoton ionization spectroscopy for state selec tive detection of the desorbing species after excitation with nanoseco nd laser pulses. The goal of our experiments was to study the influenc e of surface electronic modifications via alkali adsorption on the pho todynamics of a simple molecule. The photochemistry of the isolated an d the coadsorbate systems is strongly dependent on the coverage of the diverse components. In this paper we shall mainly focus on data for t he low coverage regime of potassium. From the two adsorbate species of NO, a chemisorbed and a physisorbed species, we present data of the c hemisorbed species. The velocity distributions show a strong dependenc e on the excitation energy which we interpret on the basis of electron energy loss spectra as being due to surface charge transfer states. T his is corroborated with our coadsorption experiments with low coverag es of potassium which alter the velocity distributions. (C) 1997 Elsev ier Science B.V.