  We examine one important (and overlooked in all previous investigations)
aspect of well - known crossing diabatic potentials or Landau - Zener (LZ)
problem. We derive the semiclassical quantization rules for the crossing
diabatic potentials with localized initial and localized or delocalized final
states, in the intermediate energy region, when all four adiabatic states are
coupled and should be taken into account. In fact these situations exhaust all
cases practically relevant for spectroscopy of non-rigid molecules (i.e. with
more than one stable configuration).

Statistical Mechanics