  Transient phenomena in quantum mechanics have been of interest to one of the
authors (MM) since long ago and, in this paper, we focus on the problem of a
potential V_- which for negative times gives rise to bound states and is
suddenly changed at t=0 to a potential V_+ which includes V_- plus a perturbed
term. An example will be the deuteron (where the proton and neutron are assumed
to interact through an oscillator potential) submitted to a sudden
electrostatic field. The analysis for t>0 can be carried out with the help of
appropriate Feynmann propagators and we arrive at the result that the
separation between the nucleons has an amplitude that depends on the intensity
of the electrostatic field, but its period continues to be related with the
inverse of the frequency of the oscillator proposed for the interaction. A
general approximate procedure for arbitrary problems of this type is also
presented at the end.
