The endothermic excitation transfer process krypton*(3PJ) + molecular nitrogen(X) -> Kr(1S0) + N2((C): a sensitive probe for the 3P2:3P0 population ratio

The excitation transfer cross section of the Kr*-N2 system has been measured in a crossed-beam experiment in the energy range 0.5 E(eV) 2.7, using a mixed beam of metastable Kr* atoms. The strongly different threshold energies (0.47 and 1.12 eV for the values J = 0 and J = 2, respectively, of total electronic angular momentum of Kr*) allow for an analysis in terms of fine-structure-dependent cross sections QJ(E), resulting in Q0 (0.94 eV) = 3.38 Å2 and Q2(2.24 eV) = 2.46 Å2 at twice the threshold energy. The slightly larger cross section for J = 0 can be explained qualitatively in terms of diabatic initial- and final-state potentials, coupled by two curve crossings with the ionic Kr+-N-2 Coulomb potential. The large difference with the experiments of Tabayashi and Shobatake, resulting in Q0 ˜ 10-2 Q2, is most likely due to a population ratio 3P0:3P2 = 1:146 in their atmospheric-arc beam source which is far from the assumed ratio 1:5 of statistical weights.