Velocity dependence of the cross section for associative ionisation of Ne atoms by laser-excited He (3¹P) atoms

The velocity dependence of the associative ionisation cross section sigma AI of Ne atoms by He(3 1 P) atoms of very short lifetime is measured in the relative velocity range 1450< nu r <3150 m s -1 (0.035<E r <0.17 eV) in a crossed-beam experiment using a slotted disc velocity selector. The 3 1 P level is obtained by laser excitation of the metastable 2 1 S level with an efficiency close to 100%. The authors observe that sigma aI ( nu r ) decreases monotonically with the increasing relative velocity of the reactants. By comparison with cross sections calculated in the framework of the classical impact parameter method, it appears that the direct process would be responsible for HeNe + ion production, while the exchange process is dominant in the total ion production.