Title: On the status of the Born-Oppenheimer expansion in molecular systems theory,
Abstract: It is shown that the adiabatic Born-Oppenheimer expansion does not satisfy
the necessary condition for the applicability of perturbation theory. A simple
example of an exact solution of a problem that can not be obtained from the
Born-Oppenheimer expansion is given. A new version of perturbation theory for
molecular systems is proposed.