Exoergic 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. 

For molecules containing a weak bond, say, HOOH, it is possible to provide enongh energy by an overtone excitation of an O—H bond so as to dissociate the molecnle. For exoergic processes it is only necessary to provide enough energy to surmount the barrier. A well-studied example is the dissociation of die cyclic peroxide tetramethyl dioxane (TMD) that fragments over a barrier of about 110 kJ mol (about three quanta of C—H stretch) to two acetone molecules... 

The parabolic assumption is critical in the prediction of an inverted region for very exoergic processes, where it shows that the rate slows down. In awarding Marcus the Nobel Prize for his work on electron transfer, the Nobel committee specifically cited this prediction. 

If A t/o > 0, the potential energy increases, that is, the elementary reaction occurs with energy absorption. These reactions are named endoergic. Note that the microscopic exoergic process can occur with either the liberation (exothermic process) or absorption of the energy (endothermic process). In this case, the sign... 

Methane biodegradation is an exoergic process that occurs in the presence of molecular oxygen. The simplified notation of methane oxidation reaction is the following ... 

These tliree effects, HCC, RE and FCC, are the main exoergic collisional process that take place in an MOT. They are the dominant loss mechanisms which usually limit the maximum attainable density and number in MOTs. They are not, however, the only type of collision in the trap. 

Free radicals generally undergo one-electron transfer processes in homogeneous solution. Two-electron transfer processes, in which two radicals participate, are often highly exoergic. Typical examples are... 

Thermodynamically the quantitative treatment of both active and passive processes requires them to be downhill or exoergic. The description of chemical potential as a function of mole fraction follows the same form as before for a neutral species (Section 8.2) ... 

Several examples of exoergic charge-transfer reactions that proceed at different rates with ground-state and electronically excited ions are listed in Table I. In some cases the cross section for the excited-state reaction may be smaller than that for the ground state, as is the case for the reactions Xe+(02, Xe)02+ Kr+(N20, Kr)N20+ Kr + (C02, Kr)COz+, whereas in other instances the excited state is more reactive, as for the processes N+(Kr,N)Kr+, N+(CO,N)CO+, 02+(Na,02)Na and 0/ (NO, 02)N0 +. The differences in reactivity are often more pronounced in the region of low ion translational energies1 lb (Fig. 10). The role of excited-state ions in charge-transfer reactions was reviewed by Hasted some time ago,175 but much more experimental data has been obtained recently, as indicated by the data shown in Table I. 

The reaction Ne + (N2,Ne)N (Table III) is the only exoergic charge-transfer process for which the Cross section has been observed to increase with increasing vibrational quantum number of the neutral reactant.128 A probable rationale for this phenomenon is that both criteria of efficient charge transfer, namely, energy resonance and favorable Franck-Condon overlap, are satisfied if the reaction entails formation of a quartet N2+ state from the (v=2) vibrational level of N2 in the ground electronic state. 

The effect of rotational energy on a reaction cross section has been studied experimentally in only one reaction, namely, Ar+(H2, H)ArH + (Table III). For this exoergic particle-transfer process, an inverse dependence of the cross section on rotational energy was observed. 

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