Recombination via Inverse Predissociation

Three potential curves participate in this mechanism (Fig. 29 c). The atoms approach each other along potential curve 1 from which radiative transition to the ground state is prohibited. This curve crosses potential curve 2 from which radiative transition to the ground state is allowed. If the non-adiabatic coupling between electronic states 1 and 2 is non-zero, the non-adiabatic transition (see Section III.9) between these states will take place (a process inverse to predissociation) and the system occurring in state 2 may radiate. Concerning this mechanism of radiative recombination see also [284]. 

The most natural theoretical treatment of this mechanism is based on the notion of Breit-Wigner resonances [78, 80, 442]. This treatment yields an expression for kj. coinciding with that obtained from the simple kinetic scheme 

It is obvious from this expression and from Fig. 29 c that this mechanism usually leads to the Arrhenius-type temperature dependence of kp with an activation energy approximately equal to the value Uc defined in Fig. 29 c. 

An illustrative example of such a temperature dependence is the atomic oxygen recombination at high temperatures (2500 — 3800 K) [323] with the overall rate constant of O2 formation in the electronic ground state corresponding to radiation over the wavelength range 2300 — 5000 A 

An example of radiative recombination via inverse predissociation without activation energy is the process 

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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... 

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