Fine-structure dependence of the Ar*(P-3(0,2))+N-2(X) excitation transfer process

Using diode lasers for the preparation of state selected beams of metastable Ar*(P-3(0), P-3(2)) atoms, the total cross section for the formation of the N-2(C, upsilon') final state has been measured for upsilon' = 0, 1,2, and 3, respectively, in a wide range of collision energies 80 < E(meV) < 2000. The energy dependence is very similar for both initial fine structure states and all final vibrational states. The experimental results are described in terms of a coupling of the initial and final state by the intermediate Ar+ + N-2(-) ionic potential, using a Landau Zener model to calculate the transition probability. Due to the similarity in shape, all cross sections are described by a single set of crossing parameters. The observed threshold energy is E(x,i) = 63 meV for both fine structure states: the contribution of the P-3(0) State does not solve the discrepancy with earlier measurements of other groups. The initial state rotation of the N-2 molecules has no influence on the shape of the cross section, as investigated by varying the rotational temperature of the supersonic target beam.