Single molecule chemistry STM

It is beyond the scope of this chapter to discuss techniques involved in STM as this important field deserves a chapter of its own. The reader should consult any of the many excellent texts devoted to this topic. 

Before discussing the examples, the notation used in Sections 2 and 3 is briefly summarized. Principal observables are the rate constant k, trapping coefficient a, 

At sufficiently low Ts 100 K, Ar residence times on the surface are sufficiently long that trapping-desorption measures desorption from a fully equilibrated Ar on the surface. In this case, measurements of Df(Ef, 6f, Ts) showed that (Ef) 2kBTs and D f(0f) is broader than cos 6f, i.e., somewhat different than the usual equilibrium assumptions [138]. However, these results are fully consistent with detailed balance and the , and 6t dependence observed for a(E, Qt, Ts) [32,138]. 

The strong chemical interaction of H with Cu(l 11) illustrates a wide variety of new chemical phenomena that are absent in the weak physisorption systems. The small mass and size of H even make some dynamic processes possible that are not present with other atom chemisorptions. 

The lowest energy atomic site for H chemisorbed on Cu(l 11) is the fee hollow site with W = 2.3 eV. Smaller and different W exists at the other high symmetry sites. Thus, the PES is very laterally corrugated, both in energy and geometry. In addition, there are metastable subsurface sites inside the surface plane, e.g., one site exists below the fee hollow with W 0.9 eV above that of the most stable surface adsorption site [140]. This is made metastable by abarrier of 0.4 eV relative to the bottom of the subsurface well. Bulk octahedral absorption sites have essentially the same stability as the subsurface sites, with presumably similar barriers to migration into the bulk. Thus, populating the subsurface site represents the initial step in bulk absorption of H. 

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