Ion pair formation in fast alkali-SF6 collisions: role of internal energy

Measurements are presented on collisional ionization of SF6 molecules in collisions with alkali atoms, using the molecular beam method. Total cross sections for the formation of negative ions were measured at collisional energies from threshold to about 30 eV, with the SF6 temperature as a parameter. The beam of alkali atoms (K, Na or Li) was produced by sputtering, velocity selected mechanically and crossed with an SF6 beam. The negative ions formed were extracted in a uniform field and mass selected. The cross sections for each specific negative ion (SF6-, SF5-, F2- and F-) show a different behavior with respect to relative energy and target temperature