Evolution of molecular states studied in collisions of ions with laser excited atoms by a crossed beam experiment

Differential scattering cross sections in the energy rangeE _CM=25–50 eV have been measured in a crossed beam machine for the scattering of Na⁺ by laser excited Na(3² P _3/2). The superelastically scattered ions resulting from the collisional deexcitation process 3² P _3/2-² S _1/2 are sharply peaked at a constant reduced scattering angle of 180eV degrees. Through the choice of either linearly or circularly polarized light, one can selectively excite the magnetic sublevels of the Na atoms. This ability to align or orient the Na^* allows us to discuss in considerable detail both the transition from the space-fixed (atomic) to the body-fixed (molecular) system and the dynamics in the merging region of the two frames. We find that the symmetry axis of the excited electron charge cloud is locked to the internuclear axis and hence to the body-fixed reference frame at an internuclear separation of about 35 a.u. A pronounced asymmetry of the scattering from atoms excited with LHC or RHC polarized light is discussed in terms of simple models.