Near resonant charge transfer in Na(4 D)+K⁺→Na⁺ + K*: optical pumping of the Na(4 D) state and energy dependence of rank 4 alignment

Rank 4 alignment has been observed in a quasi one electron system. Relative charge transfer cross sections of the Na 4 dσ, 4 dπ and 4 dδ sublevels for the K⁺+Na(4 D)→K*+Na⁺ system have been measured. A strong energy dependence is observed. The results at energies less than 1 keV may be attributed to rotational coupling of the Na 4 dπ state to the K 4 fδ state. The Na atom is excited in a two-step process, the first step being excitation to the 3²P_3/2 level with a two-mode laser to pump from both hyperfine levels of the ground state simultaneously. This two-mode laser is described in detail. The optical pumping problem is solved using rate equations. The general formula for describing the scattering intensity for cylindrical symmetry, in terms of multipole moments, for atoms excited by two linearly polarised lasers is derived and used to evaluate the experimental results.