Translational motion with electrons identified

All the analysis and discussion of the preceding subsection can now be carried over to the present situation. If perturbation theory is valid and real electronic wavefunctions are used, the lowest order contributions to the energy in growing powers of k listed in Sec. 5.1 apply also here. One, of course, has to identify the quasi-rigid motion and the soft motion in Sec. 5.1 with vibrational and rotational motion, respectively. Then, the discussion in Sec. 5.1 for cases in which perturbation theory breaks down, in particular in the presence of conical intersections, also remains valid. Where are the differences between the general analysis in Sec. 5.1 and the present one for quasi-rigid molecules First, mass polarization, see Eq. (48), contributes here in the order of. This contribution is obviously missing in Sec. 5.1, where the translational motion has not been separated off a priori. However, as discussed there, the translational motion starts to contribute... 

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