Circular Rydberg States of Lithium Atoms or Lithium-Like Ions in a High-Frequency Laser Field: The Break of the Algebraic Symmetry

Abstract

There have been publications presenting studies of relatively simple atomic systems in a high-frequency laser field. The systems studied under such a field were highly excited (Rydberg) hydrogen atoms and hydrogen-like ions, as well as highly-excited helium atoms and helium-like ions. These studies were performed classically, as appropriate for Rydberg states and revealed celestial analogies, various kinds of the precession of the electron orbit and a shift of the energy. In the current paper we analyze a lithium atom or a lithium-like ion, one of the three electrons being in a Rydberg state, subjected to a laser field of high frequency. We used the generalized method of effective potentials. We showed that for a relatively small distance of the outer electron from the nucleus, the system has higher than geometrical symmetry. For an arbitrary separation of the outer electron from the nucleus, we dealt with the broken algebraic symmetry reduced to the geometrical (axial) symmetry. We describe analytically the following two outcomes for circular Rydberg states. One of the outcomes is the precession of the plane of the orbit of the highly excited electron – the precession whose frequency we calculate analytically. It leads to the following modification of the radiation spectrum: The appearance of satellites at the distances from the unperturbed frequency of the spectral line equal to multiples of the precession frequency. The other outcome is an energy shift of the Rydberg electron. Its dependence on the nuclear charge was found to be a non-monotonic function. This is a counterintuitive result.

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