Quantum-mechanical versus semiclassical calculations of dc-field-induced tunneling rates for helium for field strengths in the range 0.067-1.0 a.u.

The dc-field-induced tunneling rates for He were computed semiclassically and quantum mechanically, the latter case being the result of the application of our previously published nonperturbative theory which accounts for electronic structure, electron correlation, and field-induced effects. As the field strength increases beyond 0.15 a.u., the deviation between the two calculations is enhanced, a phenomenon which is intrinsic to the WKB approximation and is observed explicitly, via the known expressions, in the hydrogen atom.