The UV photochem. of mols. adsorbed on metallic surfaces studied by using excimer lasers as radiation source is reviewed. Dissocn. with the fragments either ejected into the gas phase or retained on the surface is one prominent channel. The other is photodesorption of intact mols. The desorbing mols. are characterized by time-of-flight mass spectroscopy and laser spectroscopy. The state of the adsorbate after irradn. is characterized by thermal desorption spectroscopy and high resoln. EELS. The methods and fundamental characteristics are exemplified by using results from 3 systems (O2, H2O, and N2O4 adsorbed on Pd(111)). 48 Refs.