Circular Rydberg states in parallel electric and magnetic fields

Circular and nearby Rydberg states in parallel electric and magnetic fields are studied using semiclassical and exact quantum-mechanical methods. A wi de range of external field strengths is considered including regimes close to and beyond the classical ionization thresholds. When the tunneling decay rates due to the presence of the electric field are negligible, semiclassi cal eigenvalues and wave functions represent very good approximations. The combination of the complex-coordinate method with a discrete variable repre sentation and the Lanczos iterative scheme provides an efficient way to cal culate exactly the complex eigenvalues corresponding to the resonances emer ging from the quasibound circular and nearby Rydberg states. Magnetic field s have in general a stabilizing effect, diminishing the decay rates, althou gh there are cases showing the nonmonotonic (oscillatory) dependences of th e imaginary parts of the eigenvalues with increasing magnetic field strengt h. [S1050-2947(98)06012-0].