Res. Chem. Intermed., Vol. 25, No. 2, pp, 157-175 (1999) 9 VSP 1999 TEMPERATURE-PROGRAMMED ESDIAD/TOF SYSTEM AS A NEW TECHNIQUE FOR CHARACTERIZATION OF ADSORBED MOLECULES AND REACTION INTERMEDIATES TAKEHIKO SASAKI, YUICHIRO ITAI, and YASUHIRO IWASAWA* Department of Chemistry, Graduate School of Science, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113, Japan Received 20 September 1998 Abstract--A temperature-programmed (TP-) electron stimulated desorption ion angular distribution (ESDIAD) / time-of-flight (TOF) system was developed to monitor changes in adsorbed layers in real time. This system can measure ESDIAD images and TOF spectra of desorbing ions stimulated by pulsed electron beam in temperature programmed surface processes. The coadsorption layers of CO and ammonia, the coadsorption layers of CO and methylamine, and the coadsorption layer of CO and acetylene on Ru(001), which were previouslystudied by our group using LEED, TPD and HREELS, have been observed by this system. The change in configuration of admolecules, the change in site occupation and the thermal evolution of adspecies can be monitored. INTRODUCTION Real time observation in surface science and catalytic chemistry is the key issue for understanding and controlling surface reactions. Among surface science techniques electron stimulated desorption ion angular distribution (ESDIAD) has been used to investigate the conformation of adsorbates on solid surfaces [1]. Yates and co- workers have developed a digital ESDIAD system and applied it to many chemisorption systems [2]. Mass-selected ESDIAD images by adopting a pulse- gated detection system has been obtained by Madey and coworkers [3,4]. So far, most of temperature-dependent results of ESDIAD have been obtained during annealing-quenching cycles because of the rather long data acquisition time and the difficulty in the ESDIAD measurements with the simultaneous temperature control of the sample. For the purpose of monitoring surface reactions in real time using ESDIAD, we have developed a temperature-programmed (TP)-ESDIAD/time-of- flight (TOF) system which can measure ESDIAD images and TOF spectra of desorbing ions during the course of temperature programmed reactions and also at constant temperatures [5]. It is noted that TOF measurements, which are used for