Zusammenfassung
We describe a newly developed ultrahigh vacuum (UHV) experiment which
combines molecular beam techniques and in situ surface spectroscopy.
It has been specifically designed to study the reaction kinetics
and dynamics on complex model catalysts. The UHV system contains:
(a) a preparation compartment providing the experimental techniques
which are required to prepare and characterize single-crystal based
model catalysts such as ordered oxide surfaces or oxide supported
metal particles; and (b) the actual scattering chamber, where up
to three molecular beams can be crossed on the sample surface. Two
beams are produced by newly developed differentially pumped sources
based on multichannel arrays. The latter are capable of providing
high intensity 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 continuous 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 quadrupole mass spectrometer
with a liquid-nitrogen cooled ionizer housing. Time-resolved but
angle-integrated measurements are realized with a second nondifferentially
pumped quadrupole mass spectrometer. In situ measurements of adsorbed
species under reaction conditions are performed by means of an adapted
vacuum Fourier transform infrared spectrometer. The spectrometer
provides 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/desorption and reaction systems.
Nutzer