Scattering processes f alkali atoms and mols. are state selectively investigated in a scattering expt. with two crossed mol. beams. The aim of the investigation is to probe and improve the potential hypersurface. Exptl. there are measured state selective cross sections using laser spectroscopy. The system Li2(v,J)+Na is ideal for prepn. of vibrational excited states of Li2 near up to the dissocn. limit as well as for state selective measurement of scattered Li2 and the reaction product NaLi(V,J) from the endothermic reaction channel. Investigations of the total integral cross section in dependence on the vibrational excitation of the Li2 mol. probes the long range part of the interaction potential. For low vibrational states the total integral cross section shows const. values while for highly excited states Li2(v=20) the cross section is 30% greater. Comparison with quasi-classical trajectory calcns. on a LEPS potential surface shows qual. agreement but quant. disagreement. Just so the results of reactive measurements do not agree with the theor. postulates. The LEPS potential surface is not able to fit the exptl. data. In a second scattering expt. the resonance exchange interaction of differently excited like atoms was investigated. This interaction is a long range dipole-dipole interaction and scales with the inverse third power of the distance of the atoms. Classical ests. show that the exponent of the dependence on the distance of the long range potential can be extd. from the measurement of the total integral cross section with variation of the exptl. resoln. The exptl. result for Li atoms in the ground state and the first excited state verifies the expected result and agrees with quantum mech. calcns. on the well known potential hypersurfaces of the first excited state of Li2
