Abstract
The weak-field asymptotic theory (WFAT) of tunneling ionization in a static electric field is limited by the assumption that tunneling occurs from an isolated state in a compact atomic or molecular system. In this paper, we generalize the WFAT in two directions: to the cases when tunneling ionization occurs from (i) nearly degenerate states separated by a small energy distance in compact systems, and (ii) an isolated state in heteronuclear diatomic molecules at large internuclear distances . The weak-field asymptotic formulas for the ionization rates in these two cases are obtained. The asymptotics are uniform with respect to and and for sufficiently large and small , respectively, reduce to the previously known WFAT rate formula. By combining the two asymptotics, we obtain a formula for the ionization rates from the nearly degenerate and states of a homonuclear molecular ion at large internuclear distances, which is of particular interest for applications in strong-field physics. The analytical results are illustrated by calculations for several atomic and molecular models.
3 More- Received 22 June 2018
DOI:https://doi.org/10.1103/PhysRevA.98.033401
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