Endoergic process

For the three-atom reactions, none of the exoergic processes is adequately described by the theory. A possible exception is reaction (iv), for which no quantitative treatment has been published this is needed. For the endoergic processes, encouraging agreement is indicated for reaction (xv), but the detailed information available from the phase-space calculation needs to be compared with Chupka s experimental data. Experimental data are needed for reactions (v), (xvi), and (xvii). Finally, the overall shapes of the excitation functions agree well for (xi) and (xiii), but there would appear to be a significantly different behavior for (vi) at and above the reaction threshold. The two studies of four-atom reactions offer encouragement, but substantial uncertainties remain as to the validity of these comparisons. 

Analysis of published excitation functions would be greatly facilitated if they could be drawn as a function of collision energy, with laboratory energy shown on a subsidiary scale. Regretfully, this practice has not always been followed in this chapter. Whenever possible, deconvoluted excitation functions should also be published, to remove the effects of the reactant ion energy spread and the thermal motion of the target. This is particularly important for endoergic processes (see Sections 3.2.7 and... 

Direct investigations of endoergic processes " confirm the conclusions derived from the application of microscopic reversibility that is, for the usual late barriers, reactant vibrational excitation is selective in promoting reaction. However, equations (1.24) to (1.25) do not accurately relate the detailed rate constants obtained from QCL trajectory calculations performed on the same system in both directions. This is only to be expected the system is confined to quantum-state energies only right at the start of a trajectory. A product-state distribution is only derived by slicing up the continuous distribution obtained from the calculations. 

An empirical solution of Eq. (1) consists of analysis of the solvation process of the target molecule in solute, finding descriptors, which govern each phase and using them to calculate logP. This was done, for example, in the LSER approach which considered that the process of any solvation involves (i) endoergic creation of a cavity in the solvent and (ii) incorporation of the solute in the cavity with consequent setting up of various solute-solvent interactions [4—6]. Each of these steps... 

A change in a system or chemical reaction for which there is an absorption of heat (i.e., the process requires heat to proceed). In such systems, AH is a positive value (where H is the enthalpy). See also Enthalpy Exothermic Endogonic Endoergic... 

ENDOPOLYGALACTURONIDASE ENDOPOLYPHOSPHATASE Endoskeleton and exoskeleton, BIOMINERALIZATION ENDOTHERMIC PROCESS ENTHALRY EXOTHERMIC ENDOGONIC ENDOERGIC ENDOTHIAPEPSIN Endo-1,4-/J-xylanase,... 

C0+ are nonreactive. These processes have rather high endoergicities (5.5 to 5.6 eV), based on calculations for the ground-state reactants. The energies required to form the excited reactant ions in these instances ( 20 to 23 eV) are not readily accessible with ordinary photoionization sources 85 therefore, these reactions have been studied only with electron-impact ionization. The identity of the excited state responsible for the analogous reaction... 

In the projection operator formalism, which leads to a rigorous basis for the optical potential, the absorptive imaginary part is associated with transitions out of the elastic channel from which no return occurs. Whereas Pgl transitions are in this category, excitation transfer (ET) transitions are not, since return ( virtual excitation ) can occur during the ET collision. In the event that a localized avoided curve crossing with one other state dominates the inelastic process (expected for many endoergic transfers), the total absorption probability (opacity) can still be defined ... 

Table 1 summarizes several redox transformations that can be accomplished in artificial photosynthetic assemblies including the photolysis of water, carbon dioxide reduction, and nitrogen fixation processes. The endoergicities of these transformations, and the number of electrons involved in the reduction processes, are also indicated in the table. It is evident that the energy per electron to drive the various transformations are met by visible light quanta. 

C02-fixation to formate is catalyzed by formate dehydrogenase, ForDH. Photogenerated MV+ mediates the reduction of C02 to formate [200]. Other bipyridinium radicals, such as JV,j V -dimethyl-2,2 -bipyridinium or JV,Ar -trime-thylene-2,2 -bipyridinium radical cation act also as charge carriers for ForDH. The photosystem that Was utilized for generation of MV+ and 002-fixation includes Ru(bpy)f+ as photosensitizer, cysteine as sacrificial electron donor and MV2+ as electron acceptor. The net photosynthetic process accomplished in this photosystem (Fig. 40) corresponds to the reduction of 0O2 to formate by cysteine, see Eq. (70). This is an endoergic transformation by ca. 12.5 kcal mol-1. 

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