New Photoelectric Ionization Peak in the Hydrogen Atom

We present here analytical and numerical evidence which establishes that, for highly excited hydrogen atoms irradiated by microwaves, a large ionization peak occurs at frequencies much below those required for the conventional one-photon photoelectric effect. Indeed, we find that this ionization peak can, for suitable parameters values, be much higher than that of the usual photoelectric effect, a theoretical prediction which is currently being tested in the laboratory. A striking property of this ionization peak is that its frequency width is jointly determined by two independent effects: the classical chaotic threshold and the quantum delocalization border.