  In this work, we put forward a theoretical explanation of a peculiar effect
found very recently (A. Gonzalez Urena et al., Chem. Phys. Lett. 341 (2001)
495). They have observed the deflection of a beam of molecules posessing a
permanent electric dipole moment by a homogeneous electric field when a
resonant oscillating field is superposed transverse to the static one.
