Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Surface-molecule interaction general description

A simple quantum chemical description of photophysical processes involved in surface-modified metals and semiconductors was given recently by Galperin and [Pg.90]

Nitzan [18,34-36], Properties of the surface-modified semiconductor can be derived from an interaction between isolated electronic levels of the surface molecule (especially HOMO and LUMO orbitals) and the electronic continuum of semiconductor under the influence of a radiation held. The total hamiltonian (operator describing components) of the system can be formulated as a sum of hamiltonians for all the components of the system (H) and a coupling operator including all the physical processes of interest (W) (7.21)  [Pg.91]

The H 0 hamiltonian is simply a sum of the hamiltonians of individual components of the system  [Pg.91]

The above-mentioned theoretical background shows that, irrespective of the chemical nature of the photosensitizer and its binding mode to the semiconductor surface, one should consider two main ways of the semiconductor CB populating direct and indirect. Direct processes include VB - CB excitations, photosensitization via bulk doping (TTRS-driven processes) and photophysical processes involving the TTRMs term. Indirect processes, in turn, involve excitation of the surface and a subsequent electron transfer reaction (WRV1 + TTet). [Pg.91]

Apart from spectral changes, the molecule-semiconductor interaction results in modification of redox potentials on the surface species. This results from covalent bond formation between the surface of the semiconductor crystal and the molecule [44,46], [Pg.93]


The general description of the action of additives is very complicated and difficult to predict in a general manner. But it is possible to extract rules from the complex nature of the absorption process, which can guide us through the chaos. The description of adsorption by adsorption isotheims has already been described in Chapter 4. The Gibbs free energy is the characteristic quantity that describes how strongly a complex molecule will interact with metal surfaces. [Pg.221]

Insulating materials span a wide range from weakly van-der-Waals bonded molecular crystals to covalent crystals such as diamond or titanium dioxide to ionic crystals such as potassium bromide or calcium fluoride. Therefore, a general description of molecule-surface interactions is challenging in the case of insulating substrates. However, compared to metals, the interaction of organic molecules with... [Pg.195]

Now that we have a way to model the adsorption of gas species on a surface, we should consider how adsorbed species interact with a surface. There are two descriptions of molecule-surface interaction, differing mainly in terms of degree of interaction. In physisorption, molecules interact with surfaces in a weak and general way. It could be as simple as a van der Waals or dispersion interaction that keeps a molecule on a surface, like molecules of methane (CH4) or diatomic nitrogen (N2) on metal surfaces, or organic residues all over the place. Or, it could be a dipole interaction with a surface atom, which is how water molecules adsorb so easily on most surfaces. [Pg.799]

S-ProUne on Cu(110) From the section above, it can be seen that a general description of the amino acid species present in an adsorbed overlayer can be teased out from the RAIRS data, aided by a qualitative application of the metal surface selection rule. However, a major challenge exists for the field, namely, can one map the conformation and bonding interaction of each molecule to the surface. [Pg.338]

For many areas of interest the most valuable information describing the interactions between a protein and a surface is conformational change of the adsorbing protein molecule as it passes from solution to the interface. Low surface area samples in combination with some form of spectroscopic method are generally used in the evaluation of protein conformation. Recent advances in this area warrant a more detailed description of the experimental approaches. [Pg.48]

One consequence of the continuum approximation is the necessity to hypothesize two independent mechanisms for heat or momentum transfer one associated with the transport of heat or momentum by means of the continuum or macroscopic velocity field u, and the other described as a molecular mechanism for heat or momentum transfer that will appear as a surface contribution to the macroscopic momentum and energy conservation equations. This split into two independent transport mechanisms is a direct consequence of the coarse resolution that is inherent in the continuum description of the fluid system. If we revert to a microscopic or molecular point of view for a moment, it is clear that there is only a single class of mechanisms available for transport of any quantity, namely, those mechanisms associated with the motions and forces of interaction between the molecules (and particles in the case of suspensions). When we adopt the continuum or macroscopic point of view, however, we effectively spht the molecular motion of the material into two parts a molecular average velocity u = (w) and local fluctuations relative to this average. Because we define u as an instantaneous spatial average, it is evident that the local net volume flux of fluid across any surface in the fluid will be u n, where n is the unit normal to the surface. In particular, the local fluctuations in molecular velocity relative to the average value (w) yield no net flux of mass across any macroscopic surface in the fluid. However, these local random motions will generally lead to a net flux of heat or momentum across the same surface. [Pg.15]


See other pages where Surface-molecule interaction general description is mentioned: [Pg.90]    [Pg.90]    [Pg.358]    [Pg.593]    [Pg.193]    [Pg.193]    [Pg.746]    [Pg.124]    [Pg.192]    [Pg.65]    [Pg.50]    [Pg.2815]    [Pg.16]    [Pg.350]    [Pg.474]    [Pg.117]    [Pg.79]    [Pg.532]    [Pg.230]    [Pg.133]    [Pg.38]    [Pg.43]    [Pg.57]    [Pg.216]    [Pg.305]    [Pg.538]    [Pg.33]    [Pg.314]    [Pg.238]    [Pg.229]    [Pg.161]    [Pg.4728]    [Pg.221]    [Pg.458]    [Pg.573]    [Pg.113]    [Pg.320]    [Pg.231]    [Pg.6]    [Pg.229]    [Pg.209]    [Pg.425]    [Pg.2815]   


SEARCH



General interactions

Interacting Surface

Interactions description

Interactions generalized

Interactions molecule-surface

Molecule interaction

Molecules description

Surface description

Surface molecules

© 2024 chempedia.info