Collapse of the stimulated Raman adiabatic passage due to geometrical factors and how to overcome it

The adiabatic properties of stimulated Raman passage via N intermediate quasidegenerate levels are studied. It is shown that the outcome of the population transfer depends on the geometrical structure of the molecular couplings, in particular, on the signs or phases of the dipole matrix elements that connect the initial and the final states with all the intermediate levels. These phases constitute a molecular Franck-Condon configuration. The majority of the possible configurations disable adiabatic passage through a dark state so that the dynamics is dominated by Rabi oscillations among the different levels. It is shown, however, that adiabatic passage can be regained via nonresonant stimulated Raman for almost all possible configurations.