A molecular beam/surface spectroscopy apparatus for the study of reactionson complex model catalysts

We describe a newly developed ultrahigh vacuum (UHV) experiment which combi nes molecular beam techniques and in situ surface spectroscopy. It has been specifically designed to study the reaction kinetics and dynamics on compl ex model catalysts. The UHV system contains: (a) a preparation compartment providing the experimental techniques which are required to prepare and cha racterize single-crystal based model catalysts such as ordered oxide surfac es or oxide supported metal particles; and (b) the actual scattering chambe r, where up to three molecular beams can be crossed on the sample surface. Two beams are produced by newly developed differentially pumped sources bas ed on multichannel arrays. The latter are capable of providing high intensi ty and purity beams and can be modulated by means of a vacuum-motor driven and computer-controlled chopper. The third beam is generated in a continuou s or pulsed supersonic expansion and is modulated via a variable duty-cycle chopper. Angular and time-resolved measurements of desorbing and scattered molecules are performed with a rotatable doubly differentially pumped quad rupole mass spectrometer with a liquid-nitrogen cooled ionizer housing. Tim e-resolved but angle-integrated measurements are realized with a second non differentially pumped quadrupole mass spectrometer. In situ measurements of adsorbed species under reaction conditions are performed by means of an ad apted vacuum Fourier transform infrared spectrometer. The spectrometer prov ides the possibility of time-resolved measurements and can be synchronized with any of the beam sources. This contribution provides a general overview of the system and a description of all new components and their interplay. We also present test data for all components employing simple adsorption/d esorption and reaction systems. (C) 2000 American Institute of Physics. [S0 034-6748(00)04011-9].