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 simpleatomic systems in a high-frequency laser field. The systems studied under sucha field were highly excited (Rydberg) hydrogen atoms and hydrogen-like ions, aswell as highly-excited helium atoms and helium-like ions. These studies wereperformed classically, as appropriate for Rydberg states and revealed celestialanalogies, various kinds of the precession of the electron orbit and a shift ofthe energy. In the current paper we analyze a lithium atom or a lithium-likeion, one of the three electrons being in a Rydberg state, subjected to a laserfield of high frequency. We used the generalized method of effectivepotentials. We showed that for a relatively small distance of the outerelectron from the nucleus, the system has higher than geometrical symmetry. Foran arbitrary separation of the outer electron from the nucleus, we dealt withthe broken algebraic symmetry reduced to the geometrical (axial) symmetry. Wedescribe analytically the following two outcomes for circular Rydberg states.One of the outcomes is the precession of the plane of the orbit of the highlyexcited electron – the precession whose frequency we calculate analytically. Itleads to the following modification of the radiation spectrum: The appearanceof satellites at the distances from the unperturbed frequency of the spectralline equal to multiples of the precession frequency. The other outcome is anenergy shift of the Rydberg electron. Its dependence on the nuclear charge wasfound to be a non-monotonic function. This is a counterintuitive result.