Momentum theorems for electrons in the presence of monochromatic radiation and intramolecular perturbations

Conservation of electronic mechanical momentum in a molecule perturbed by periodic fields is discussed within the quadrupole approximation, i.e. assuming a spatially uniform magnetic field and electric field gradient. It is shown that the induced momentum is related to the electric polarizabilities of the electron distribution. Intramolecular static perturbations arising from nuclear magnetic moments and quadrupole moments are discussed.