A temperature-programed (TP) electron-stimulated desorption ion angular distribution (ESDIAD)/time-of-flight (TOF) system was developed in order to observe surface processes in real time by ESDIAD images and to measure TOF spectra of desorbing ions for identification of the mass and the kinetic-energy distribution of ions. The instrumentation of this system is described. This system was applied to(&sqrt3;×&sqrt3;)R30°-CO/Ru(001)(0.33 ML) and CO-saturated Ru(001) surfaces. As for the(&sqrt3;×&sqrt3;)R30°-CO/Ru(001),the increase of the half width at half maximum of the ESDIAD images upon annealing was found corresponding to the thermal excitation of the bending mode and/or hindered translation. On the other hand, as for the CO-saturated surface, the static disorder of the molecular axis of CO was larger, and apparent thermal excitation was not observed. After partial desorption of CO from the CO-saturated surface where the surface changes into the&sqrt3;×&sqrt3;structure at 400–430 K, the yield ofO+increased due to the change in the adsorption site of CO. TOF spectra for ammonia adlayers(NH3andND3)were also measured by the developed system and the isotopic ratios for ESD yields depending on the adsorption states (chemisorbed first layer and physisorbed second layer) were obtained. ©1998 American Institute of Physics.