PREDICTION OF A NEW PEAK IN 2-FREQUENCY MICROWAVE IONIZATION OF EXCITED HYDROGEN-ATOMS

We report the first theoretical and experimental study of the detailed frequency dependence of the ''ionization'' of excited H atoms by a tw o-frequency (2f) microwave field. Our ID quantal and 1D classical calc ulations, in excellent agreement with each other, predict a new 2f ion ization peak. The peak scales classically. We present a model which sh ows that the location and the width of the peak are determined by clas sical phase-space structures. The theoretical results are supported by experimental data with 3D atoms.