Angular momentum general theory

The theory of Section 1.8 is sometimes qualified as non-Markovian since it accounts for non-exponential angular momentum relaxation, unlike impact theory which is Markovian in this sense. However, it is not a unique non-Markovian generalization of impact theory. Not less known is a differential version of the theory... 

Relations (2.46) and (2.47) are equivalent formulations of the fact that, in a dense medium, increase in frequency of collisions retards molecular reorientation. As this fact was established by Hubbard within Langevin phenomenology [30] it is compatible with any sort of molecule-neighbourhood interaction (binary or collective) that results in diffusion of angular momentum. In the gas phase it is related to weak collisions only. On the other hand, the perturbation theory derivation of the Hubbard relation shows that it is valid for dense media but only for collisions of arbitrary strength. Hence the Hubbard relation has a more general and universal character than that originally accredited to it. 

In this section we extend the theory of photodissociation and rotational excitation outlined in Section 3.2 for J = 0 to general angular momentum states J 7 0 of a triatomic system ABC. We will closely follow the detailed presentation of Balint-Kurti and Shapiro (1981) [see also Hutson (1991), Glass-Maujean and Beswick (1989), Beswick (1991), and Roncero et al. (1990)]. The discussion in this section is not meant to be a substitute for reading the original literature we merely want to outline the general methodology and underline the complexity of the theory. 

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