Calorimeter for adsorption energies of larger molecules on single
crystal surfaces
Review Of Scientific Instruments, 75 (11):
4471--4480 (November 2004)DOI: 10.1063/1.1794391
Abstract
A calorimeter for measuring heats of adsorption of large molecules
on single crystal surfaces is described. It extends previous instrumentation
for single crystal adsorption calorimetry by adding the capability
for measuring larger (lower vapor pressure) molecules. This is achieved
using a chopped and collimated (similar to4 mm diameter) molecular
beam capable of stable 100 ms pulses of low vapor pressure substances,
and a line-of-sight modification of the King and Wells method for
measuring their sticking probabilities at the single crystal's surface.
The heat input to the single crystal due to adsorption is detected
using a pyroelectric polymer ribbon pressed against the back of the
single crystal, following our previous calorimeter design. Measurements
of benzene adsorption on Pt(111) prove the capability to produce
a highly stable beam of flux similar to2x10(14) molecules/(cm(2)
s) and measure adsorption energies with an absolute accuracy of similar
to5% and a pulse-to-pulse standard deviation of 2 kJ/mol. (C) 2004
American Institute of Physics.