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

Using diode lasers for the preparation of state selected beams of metastable Ar ∗( 3P 0, 3P 2) atoms, the total cross section for the formation of the N 2(C, v') final state has been measured for v' = 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 Ex,i = 63 meV for both fine structure states: the contribution of the 3P 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.