Recombination on a Repulsive Potential Curve

In this case, the recombining atoms approach each other along a repulsive potential curve 1 (see Fig. 29 a) and, according to the Franck-Condon principle, emit a photon hv near the classical inflection point R, forming a molecule in the ground 

It is seen from Eqs. (19.2) and (19.3) that when molecular states 1 and 2 converge, i.e. correlate with the same atomic states, rather rapidly (as T with n 3) increases with temperature and the probability will be much smaller than 10 predicted above. The latter is due to the low frequency of radiation (of the order kT/h) emitted in this case. 

Any experimental data on radiative recombination proceeding by such a mechanism are lacking. However, theoretical calculations on H [23] and 2 [247] (first two systems of Table 5) support these conclusions. The extremely low values of kj. for F2 s re due to the very small value of the transition dipole moment in this case. 

The location of the potential curves for this case is illustrated in Fig. 29 b. Here the atoms can reach the inner limb of curve 1 where, according to the Franck-Condon principle, radiative transition to curve 2 yields a molecule with a low vibrational quantum number. Therefore, the probability depends mainly on the transition dipole moment close to the equilibrium distance Rg of the ground state, di2(Rt) di2(Re). In this situation, the available information about photodissociation may be used to calculate kr according to the principle of detailed balancing. 

The order of magnitude estimation of k can be obtained using a simple expression derived in [226] 

---

Fig. 29 a—c. Potential energy curves corresponding to different mechanisms of radiative recombination, a Recombination on a repulsive potential curve, b recombination on an attractive potential curve, c recombination via inverse predissociation... 

---