L. Lian et al., SIZE DEPENDENCE OF MOBILITY ON THE SURFACE OF METAL-CLUSTERS - AMMONIA ON AG-10 AND AG-16, The Journal of chemical physics, 104(13), 1996, pp. 5338-5344
Equilibrium constants for the reactions of NH3 with the silver cluster
s, Ag-10 and Ag-16, have been measured in the gas phase as a function
of temperature using a cluster flow reactor. The binding enthalpies, D
elta H(300)degrees = -9.8 +/- 1.0 and -15.9 +/- 1.0 kcal mol(-1), and
entropies, Delta S(300)degrees = -10.3 +/- 3.0 and -23.5 +/- 3.0 cal m
ol(-1) K-1, have been obtained for the complexes Ag10NH3 and Ag16NH3,
respectively. Statistical mechanics modeling indicates that NH3 is mob
ile on the surface of Ag10NH3. In contrast, it is locally bound on Ag-
16. The implication is that the binding mechanism involves only electr
ostatic interaction on Ag-10 and that Ag-16 provides a site favorable
to a stronger classical chemical lone-pair bond. Thus ammonia may diff
use on Aglo and be localized on Ag-16. (C) 1996 American Institute of
Physics.