Isolated-core quadrupole excitation of highly excited autoionizing Rydberg states

Abstract

The structure and photoexcitation dynamics of high lying doubly excited states of the strontium atom with high angular momenta are studied in the vicinity of the Sr${}^{+}(N=5)$ threshold. The spectra recorded using resonant multiphoton isolated core excitation are analyzed with calculations based on configuration interaction with exterior complex scaling, which treats the correlated motion of the two valence electrons of Sr from first principles. The results are rationalized with a model based on multichannel quantum-defect theory and transition dipole moments calculated with a perturbative treatment of electron correlations. Together, both approaches reveal that most of the lines observed in the spectra arise from the interaction of a single optically active state, coupled to the initial state by an electric-dipole transition, with entire doubly-excited Rydberg series. The long-range electron correlations responsible for this interaction unexpectedly vanish for identical values of the initial and final principal quantum numbers, a fact related to the quasi hydrogenic nature of the high-$l$ Rydberg electron. This special situation, and in particular the vanishing interaction, leads to the surprising observation of an electric \emph{quadrupole} isolated-core excitation with a similar intensity as the neighboring electric dipole transitions.

11 pages, 5 figures

References in corpus (4)

• Controlling Rydberg excitations using ion core transitions in alkaline earth atom tweezer arrays
• Optical coherent manipulation of alkaline-earth circular Rydberg states
• A Coherent Light Shift on Alkaline-Earth Rydberg Atoms from Isolated Core Excitation without Auto-Ionization
• Structure and electron dynamics of planetary states of Sr below the Sr${}^{+}$ $7d$ and $8p$ thresholds

Cited by in corpus (2)

• Autoionization of high-$\ell$ core-excited Rydberg states of alkaline-earth-metal atoms
• Series of molecular-like doubly excited states of a quasi-three-body Coulomb system