Anticrossing effects in Rydberg states of lithium in the presence of parallel magnetic and electric fields

Rydberg states in lithium have been excited from the ground state by absorption of {π}-polarized photons in the presence of parallel electric F and magnetic B fields. The magnetic field strength (B=3.11 T) is high enough to reach the inter-n-mixing regime, and a small electric field strength (F{}25 V/cm) is sufficient for the lowest state of the n=30 manifold to penetrate into the high-energy part of the n=29 manifold. The first anticrossing is thoroughly studied. Away from the anticrossing the spectrum exhibits two lines, but at the anticrossing a third component appears in the structure in the same energy range. This provides an experimental confirmation for the existence of pairs of almost-degenerate states with opposite parities in the high-energy part of the diamagnetic manifold of lithium. The two components of this doublet behave differently at the anticrossing. The experimental data have been interpreted in a global treatment in which core effects and intermanifold couplings are simultaneously taken into account. The different behavior of low- and high-lying states of the multiplet with respect to these two interactions is analyzed in detail.