Coherent excitation of multilevel quantum systems by adiabatic application of an external resonance field

An analysis is made of the published results of an experimental study of the excitation of rotational states of molecules by an external resonance field. Some features of such excitation can be explained if the external field is switched on and off not instantaneously but adiabatically. In view of the adiabatic conditions an increase in the detuning of an external field should reduce the observed signal at a rate faster than that proportional to the reciprocal of the square of the detuning.