Alignment-orientation transition at optical excitation of molecules in magnetic field

Angular momentum alignment-orientation transition is analyzed for the ground state of diatomic or linear molecules subjected to the dynamic Stark effect. Analytical expressions are derived for the orientation value. It is shown that, first, orientation of angular momenta resulting from the action of the dynamic Stark effect is a nonlinear process which depends quadratically on the intensity of the irradiating light; second, it is a quantum effect and disappears for the states with large angular momenta; and, third, it occurs only in the presence of an external magnetic field.