The radiative recombination of atoms

It is clear both experimentally and theoretically that the radiative recombination of two atoms, without a third body, is an improbable process. Experimentally, such 

In the study of any radiative recombination process, one tries to answer a number of fairly well defined questions, mostly related to potential curves. From what electronic states is emission observed With what atomic states do these molecular states correlate Does the recombination take place on a single potential curve, or is a transition between two curves involved Is a potential curve with a significant maximum involved Is a third body necessary, either to stabilize the atom pair on a single curve, or to induce a transition to another curve In the case of a transition between two electronic states, is there an approximate equilibrium What is the vibrational and rotational distribution of newly formed molecules What is the recombination rate coefficient as a function of temperature or cross section as a function of energy In principle these questions can be answered either theoretically or experimentally. In fact, they have been answered experimentally in most cases, but the answers are seldom as certain or as numerous as one would wish. This becomes clear in the following discussion of particular cases. 

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