Ionization of hydrogen atoms with principal quantum number n =32, 40, and 51-74^by a 9.92-GHz electric field F(/) = z/ocoscof was studied with a superimposed static electric field F s = 0, 2, 5, and 8 V/cm. The measured field strengths Fo(\0°/o) at which 10% of the atoms were ionized are in excellent agreement with classical calculations in both one and two spatial dimensions. Covering finer detail as well as gross structure of the n dependence of FoOOo/o), the agreement supports the application of classical dynamics to the analysis of this strongly perturbed quantum system.

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Spin polarization symmetries of Dirac particles in the presence of (1 +_fi)V(r) potentials are discussed. The effects of a symmetry breaking term eV(r) are explored and applied to proton and anti-proton scattering on nuclei in the framework of Dirac optical models.