Physisorbed hydrogen

Persson M, Wiizen L and Andersson S 1990 Mean free path of a trapped physisorbed hydrogen moiecuie Phys. Rev. B 42 5331... 

Instrument. Before the H2 chemisorption, each sample was heated in pure H2 at 300°C for 90 min, subsequently it was heated in He at 290°C for 60 min in order to desorb hydrogen from the sample. The chemisorption measurement was performed at 0°C by several H2 pulses with an Ar purge in between, in order to desorb physisorbed hydrogen. A 1/1 H/Pt ratio was used to estimate the Pt dispersion. Values in the range 50-70% have been obtained on the fresh samples Pt—Ba/ y-Al203 (1/20/100 w/w) catalyst. 

The understanding of the relationships between molecular structure of tailored organic molecules, their hierarchical organization in assemblies chemically bound to surfaces and interfaces as well as their fimctionality represent fundamental topics of current interest [104,105]. hi the following we shall focus on so-called chemisorbed, self-assembled monolayers (SAM), which are distinctly different from the physisorbed, hydrogen-bonded adlayers discussed in the previous paragraph. Following a historical development we will use the terminus self-assembled monolayers herein exclusively as molecular assemblies formed by chemisorption of an active surfactant onto a solid surface [106-108]. We will specifically focus on selected results with aromatic SAMs on Au(lll) electrodes at solid-liquid interfaces. 

Faradaic admittance experiments on a mercury surface blocked by tribenzy-lammine [208] and in situ STM experiments with physisorbed hydrogen-bonded monolayers of guanine and adenine on HOPG [209, 210] revealed an average... 

Step 2 surface dissociation of physisorbed hydrogen molecules into H ad-atoms The activation energy must be sufficient to overcome the energy required to form a hydrogen-metal bound. This activation energy is due to the repulsion between the electrons of the hydrogen molecule and surface electrons of the metal. Therefore, the activation energy depends on the chemical composition at the surface of the metal. 

TABLE 3.2 Diffusion Constant D(T) in cm /sec Obtained in [5 for Physisorbed Hydrogen Diffusion on a Cu(111) Surface... 

---