1. It is emphasized that this relation is consistent with the basic physical assumptions as well as with the recommended rate constant formulations. In contrast to the modified Ford model the quantity z t of the proposed model is dependent on Tvib,iand thus on the vibrational excitation of the molecular species Xi. Moreover, even an equal probability assumption (U =m)yields transformed energy amounts GUa,iwhich are clearly greater than ,ib,i.As a consequence of this modeling, also exchange reactions influence the chemistry-vibration coupling and not only, as previously assumed, dissociation reactions. Figure 5 exhibitsthe resultsjust pointed out. There the pseudetemperature U is selected to be a fraction of the dissociation energy. If we regard a dissociation reaction with A being identical to Diand select cr = 1,expression (49) reduces to the simple relationship 2, = L;'(T)which has already been proposed by Marrone '. Thesecondspecial case, a reaction with zero activation energy, leads to the relationship G&=: = L D ' ( ). Only in the case Fig. 5: The average vibrational energy lost from disintegrations of NO molecules in an exchange reaction with respect to the universal gas constant plotted over the vibrational temperature Tvib,0 at T =20000Kin dependence on U (a= 1)
2. In the case of vibrationally little excited molecules (Tvib,<< T)this value of G:dpPi(-)ismuch greater than the value of ;(ri), even if U =co.Corresponding to this theory the value of in Figure 5 is determined by the huge value of T = Tvib,NO= 20000 I< also if Tvib,vO<< 20000I< Physically this means that formation processes substantially raise the vibrational temperature of the regarded molecular species Xi. As a consequence of this fact, e.g. recombinations would accelerate the equilibration process of TVib, and T or would even lead to a distinct overshoot of vibrational temperature over T. We think critically about this theory and suppose that disintegration as well as formation of a molecule occur from or up to a certain vibrational state 1with the same probability. In other words, if a molecule is more likely to disintegrate if it is in a higher vibrational state, that molecule is more likely to come into existence in a higher vibrational state too, and not in a still higher one. The equilibrium condition Gz;p,i = G: is also fulfilled when setting
3. Schmeltekopf has experimentally determined the backward rate constants for the endothermic charge exchange reaction NO+ +N +N2+0+forT=300K and Tvib,N2 ranging from 300 to 6000 K ". He disc+ vered that the reverse reaction rate rises very steeply as the vibrational temperature Tvib,N2is raised above 1000 K (up to a factor 50). This experimental result justifies the proposed nonequilibrium factor qsfor reverse reactions with molecular participation. However, in order to reproduce these measurements by means of our modeling, the probability parameter U in the description of Q5must be selected as a function of Tvib,N, Setting U = 900fr'+0.77Tuib,N,yields the best agreement with experimental data. Physically this means that the less the molecules are vibrationally excited the less likely is a reaction from lower vibrational energy levels to occur. In Figure 6 both experimental and calculated results are presented. O'Malley also calculated the backward rate constants for the above reaction by means of a theoretical scattering model ranging from 300 to 7000 I( for both T and TUib .br 2 Il. His calculations yield the same qualitative results as above and are fitted best by selrcting U = O.75T +x,b,n- for temperatures T > 2000 I< Figure 6 also contains one of these results and in addition shows an extrapolation of this modeling to a heavy particle temperature of T = 12000I<
4. 2 1o-2 6.2 Relaxation of Pure Nitrogen