Examples from this laboratory illustrating laser probing of gaseous products formed in chemical reactions on surfaces are taken from the areas of catalytic reactions, silicon etching, and surface photochemistry. The emphasis will be on the unique advantages of laser diagnostics in these dynamical and mechanistic studies in which the chemical reaction product species undergo no collisions after leaving the surface before detection by the laser. UHV experiments on the catalytic oxidation of H2, D2 and NH3 by N02 and H2 by NO2 used the laser-induced fluorescence (LIF) technique to measure the apparent desorption energies of OH radicals and the rotational energy accommodation of the desorbing OH, OD and NO reaction products. The observed different degrees of "rotational cooling" in the different products will be discussed. In multiphoton ionization mass spectrometry experiments (MPI/MS) spectroscopies of three different MPI processes for the SiF2 radical were studied and two of these were applied to the study of silicon etching by XeF2, F2, and NF3. The only observed gaseous products were SiF4 and the SiF2 radical and their apparent production energies correlated with the case of surface fluorine atom production. In the area of surface photochemistry, an excimer laser was used to photolyze iodobenzene, trimethylgallium, and copper acetylacetonate adsorbed on a cold surface. The time-of-flight (TOF) spectra of the fragments or reaction products were measured by using a mass spectrometer equipped with multiphoton (MPI) or electron (EI) ionization.