Hydrogen atom in crossed magnetic and electric fields.

The first studies with the hydrogen atom in strong crossed magnetic and electric fields are reported. Long-living states reaching well above the Stark saddle energy are discovered. They are quantitatively explained by second-order perturbation theory, indicating regular, nonchaotic dynamics in these states. Fourier-transformed spectra and classical trajectory calculations indicate the existence of periodic orbits high in the field ionization regime. Sensitive spectral dependence upon the angle between the fields due to symmetry breaking is observed and accounted for by second-order perturbation theory.