Fine structure and Zeeman effect in the triplet state of6Li 2 by Doppler-free polarization spectroscopy

Abstract

The low-lying triplet states of the lithium dimer are of particular interest because of their role in the predissociation of states correlating with the 22S112 +22P3a,la atomic states of Li. In this work, the fine structure of the b(1)3H state of 6Li2 is investigated using Doppler-free polarization spectroscopy. The triplet state is accessed using one of the rare singlet-triplet intercombination transitions. In such a transition only one of the triplet fine structure sublevels receives intensity through spin-orbit interaction with the A1EJ state. However, the remaining two fine structure levels can be excited by using the Zeeman interaction to mix levels of different J. Two polarization geometries were used in separate experiments to study different groups of M levels in magnetic fields up to 3 kG. An irreducible tensor derivation of the fine structure and Zeeman Hamiltonian matrix in Hund's case (b) symmetrized basis functions was used to find the electronic perturbation parameters and the spin-spin and spin-rotation fine structure constants by a fit to the Zeeman splitting pattern. In the particular case presented here (levels with high J), the spin-orbit contribution to the fine structure was too small to be accurately determined. However, the electronic singlet-triplet spin-orbit interaction could be found with high precision.