Inner-electron ionization of Sr5s16lstates

Abstract

We have measured the probability of inner-electron ionization (IEI) of Sr $5s16l$ atoms when exposed to intense 230-fs laser pulses. We find that the probability of IEI rises sharply at $l=5$ and is approximately equal to one for $l>5$. For $l=5$ the classical inner-turning point is at ${15a}_{0}$, far greater than the size of the Sr${}^{+}$ ionic core, ruling out core penetration as the factor governing inner-electron ionization. For the Sr ${5p}_{1/2}16l$ states of $l>5$ the autoionization lifetime, which is due to the electrostatic interaction between two-valence electrons, is greater than the Kepler orbit time. These comparisons suggest that both inner-electron ionization and autoionization are governed by long-range electrostatic interactions.