Theoretical investigations on the Stark-Zeeman effect of the 2p 2P3/2-level in Li6 for perpendicularly crossed fields

The splitting behaviour of the 2p 2P3/2 hyperfine structure levels is investigated in Li6 for homogeneous crossed electric and magnetic fields (Stark-Zeeman effect). This is done by diagonalizing the perturbation matrix comprising the hyperfine interaction, the electronic and nuclear magnetic interaction and the effective electric interaction obtained by transforming the quadratic Stark effect to a first order perturbation interaction. Symmetries are used to find analytic formulae for level shifts and crossing points if only one external field is present. A reflection symmetry unbroken with all 3 interactions present permits the decomposition of the 12 x 12 matrix into two 6 x 6 sub-matrices. The structure of energy eigenvalue surfaces εF,MF(B,E) of the two subsystems is found by numeric diagonalization of the perturbation matrix and is displayed in the ranges |B|< 1 mT, |E| < 300 kV/cm. The total angular momentum F = J + I (J = 3/2, electronic angular momentum, I = 1, nuclear spin) and the magnetic quantum number MF provide labels for all surfaces. All crossing points of the energy surfaces have been found. Adiabatic level transfer occurring in atoms traversing a sequence of crossed magnetic and electric fields is explained. Berry phases occur for cycles around some crossing points. Their presence or absence is explained. (authors)