Detachment processes in low-energy Br-, I--He collisions

Doubly differential cross sections (DCS) for detachment in Br-, I--He collisions are reported in the 10-18 eV centre of mass energy range. Use of a supersonic beam as a target allows a strong reduction of the thermal broadening which usually affects energy loss measurements in heavy-projectile-light-target collisions. The simultaneous measurements of laboratory scattering angles and energy losses led to an unambiguous determination of the differential cross sections. At the lowest energies (ECM<or=12 eV) the cross sections present a single maximum whereas with increasing energy, an oscillating structure which is interpreted as a 'Stueckelberg' interference phenomenon occurs in the continuum. It is suggested that the behaviour of the electron spectra as a function of the scattering angle could be explained along the same lines.

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