NONADIABATIC EFFECTS IN RYDBERG STATES AND THEIR MANIFESTATION IN MULTIPHOTON IONIZATION OF MOLECULES G.K.Ivanov, G.V.Golubkov N.N.Semenov Institute of Chemical Physics, Russian Academy of Sciences Kosygin str. 4, Moscow 117977, Russia We consider the strong field perturbation of interacting Rydberg series np0 and np2 populated under multiphoton ionization of H_2 molecules. Peculiarities of the stabilization effect in molecular system are discussed