DYNAMIC TUNNELING IONIZATION OF EXCITED HYDROGEN-ATOMS - A PRECISE EXPERIMENT VERSUS THEORIES

New data for n0 = 24,...,32 H atoms ionized by a linearly polarized, 9.908-GHz electric field are compared with calculations. Being more precise than laser multiphoton ionization experiments with tightly bound atoms, our experiments distinguish between tunneling through and classical escape over a slowly oscillating barrier and between one- and many-state dynamical processes. Formulas used to interpret low-frequency laser multiphoton ionization data poorly describe our results. Our data delineate ranges of validity of other partly successful models and are best reproduced by a new 3D semiclassical model.