Electron Diffraction Determination of Nanoscale Structures Page: 4 of 20
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A. Adsorption of H2O and 02 on gold cluster cations and anions.
Based on the understanding of gold cluster structures, experimental and theoretical
investigations of gold cluster anions present a unique opportunity to correlate sizes and structures
with catalytic reactivity on an atom-by-atom level. This section describes the initial
measurements which characterized the chemisorption of water and oxygen molecules on gold
cluster anions and cations. The results clearly identified correlations between chemisorption
reactions and cluster structures.
Adsorption measurements are performed by admitting the reactant gas into a quadrupole ion
trap after a particular cluster ion size is mass selected and thermalized at the temperature of a
background helium gas. The equilibrium product species, AunXX and AunXX+, are mass analyzed
by ejecting the trapped product ions into a channeltron detector after long exposures to the
A.1. Gold cluster anion complexes with oxygen
Figure 1 displays multiply adsorbed 02 molecules at 150 K, po2=10-4 Torr, and exposure time
of 50 s. Odd number sizes show weaker adsorption of only a single 02. Best fit structures are
shown for the two most strongly adsorbing cluster sizes at n=20 and 22. Beam experiments16
exhibited only singly adsorbed 02 on even number sizes and identified correlation of the
adsorption strength with electron affinity.
[A U 22~X]-
6 8 10 12 14 16 18 20 22 24 26
n (cluster size)
Figure 1. Multiply adsorbed 02 molecules on gold cluster anions. Black
rectangles indicate single 02 molecule adsorption and blue rectangle
indicates adsorption of 2 molecules. Insets show structures and enlarged
mass spectra of [Aun(O2)x]- complexes for n=20 and 22.
x= 0 2
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Parks, Joel H. Electron Diffraction Determination of Nanoscale Structures, report, March 1, 2013; United States. (digital.library.unt.edu/ark:/67531/metadc836528/m1/4/: accessed February 17, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.