Energy transfer theoretical considerations

Photoelectrochemical experiments on the pyrite/H2S system, as well as theoretical considerations, led Tributsch et al. (2003) to the conclusion that CO2 fixation at pyrite probably could not have led to the syntheses proposed by Wachtershauser. The reaction mechanism involved in such reactions is likely to be much more complex than had previously been assumed. The Berlin group supports the objection of Schoonen et al. (1999) that, apart from other points, the electron transfer from pyrrhotine to CO2 is hindered by an activation energy which is too high. There is, thus, no lack of different opinions on the model of chemoautotrophic biogenesis hopefully future studies will shed more light on the situation ... 

The photofragmentation that occurs as a consequence of absorption of a photon is frequently viewed as a "half-collision" process (16)- The photon absorption prepares the molecule in assorted rovibrational states of an excited electronic pes and is followed by the half-collision event in which translational, vibrational, and rotational energy transfer may occur. It is the prediction of the corresponding product energy distributions and their correlation to features of the excited pes that is a major goal of theoretical efforts. In this section we summarize some of the quantum dynamical approaches that have been developed for polyatomic photodissociation. For ease of presentation we limit consideration to triatomic molecules and, further, follow in part the presentation of Heather and Light (17). 

Secondly, the rate coefficients of unimolecular bond fissions and of bimolecular combinations depends, not only on the temperature, but also on the concentrations of the species which are not chemically transformed by the elementary process under consideration, but which play a role in energy transfer processes. Various theoretical treatments of this effect have been suggested (see, for example, refs. 1—15). 

The mechanism for impact scattering at solids is rather complex as it involves the penetration of the incident electron into the adsorbed molecule the theoretical treatment requires a quantum mechanical formalism. The transfer of energy from the incident electron to a vibrational mode occurs, within a very short time, while the electron is inside the molecule. The dipole-scattering selection mles do not apply to impact scattering. Theoretical considerations have predicted, and experimental studies have confirmed, the following propensity mles for this mechanism" (i) Impact scattering... 

Knox R. Exciton energy transfer and migration theoretical considerations. In Bioenergetics of Photosynthesis. Govindjee ed. 1975. Academic Press, New York. pp. 183-221. 

Although the calculations of the transition energies of different tautomeric forms of molecules have been performed in a few cases, the discussion has been restricted to the difference in electronic absorption band positions and not to the change in relative stabilities of the tautomers caused by electronic excitation. The latter problem, however, has been the subject of a few theoretical considerations for nucleic acid base pairs. Most of these studies were motivated by the need for a potential function for double proton transfer between nucleic acid bases that would allow calculation of proton tunneling probabilities for the Lowdin model of mutagenesis (Lowdin, 1965). 

We have defined the solvation process as the process of transfer from a fixed position in an ideal gas phase to a fixed position in a liquid phase. We have seen that if we can neglect the effect of the solvent on the internal partition function of the solvaton s, the Gibbs or the Helmholtz energy of solvation is equal to the coupling work of the solvaton to the solvent (the latter may be a mixture of any number of component, including any concentration of the solute s). In actual calculations, or in some theoretical considerations, it is often convenient to carry out the coupling work in steps. The specific steps chosen to carry out the coupling work depend on the way we choose to write the solute-solvent interaction. 

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