Reversible electronic relaxation, vibrational

On pp 289-310 (Ref 21), A.G. Gaydon, Shock-Tube Studies of Processes of Electronic Excitation in Gases reported that the spectrum-line reversal temperature in shock-heated gases can be used to obtain information about efficiencies and processes of electronic excitation of metal atoms at high temperatures. For excitation by molecules, the electronic excitation temperature tends to follow the effective vibrational temperature of the molecules, and reversal temperatures may be low near the shock front if. the vibrational relaxation time is appreciable. Although excitation of metal atoms by cold inert gases has a very small effective cross-section, it is shown that at 2500°K the cross-sections of excitation of Cr or Na by Ar or Ne are around 1/20 of the gas-kinetic cross-sections... 

In this paper, the multiphonon relaxation of a local vibrational mode and the non-radiative electronic transitions in molecular systems and in solids are considered using this non-perturbative theory. Results of model calculations are presented. According to the obtained results, the rate of these processes exhibits a critical behavior it sharply increases near specific (critical) value(s) of the interaction. Also the usual increase of the non-radiative transition rate with temperature is reversed at certain value of the non-diagonal interaction and temperature. For a weak interaction, the results coincide with those of the perturbation theory. 

Equation (7) disregards the possibility of atom recombination in the presence of electrons (i.e. the reverse of processes XIV) while the influence of atoms on the vibrational relaxation comes from terms P +1 NHN and so on in the different equations. Eqs. (10a) and (10b) are a direct consequence of the detailed balance applied to Eqs. (XII)-(XIII), while Keq and Qv represent the equilibrium constant of the process H2 i 2H and the vibrational partition function of H2 respectively. These values have been taken from12). 

The rates k/ and k correspond to any nonradiative decay channel, which couple to the levels /) and /n). It should be kept in mind, however, that reverse collisionally induced electronic transitions may follow vibrational relaxation in the /) manifold, thus leading to further emission. This effect must be taken into account when the jj) level is not the lowest one in the j>) manifold (see Section III.B). 

No dependence of on [Q2] was found for emission from higher vibrational levels of the B state whereas Ix — AtJCh] was found for emission from lower levels. It was concluded that Qj was effective in relaxing higher vibrational levels to lower levels of the B state, and that lower levels were more effectively electronically quenched by chlorine atoms, giving an order < 1 in [Oa] for low vibrational levels. It was argued that the reverse of reaction (8) can occur for higher vibrational levels near the dissociation limit before the product is stabilized by thermonuclear collision to low levels of the B state. 

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