Cross sections and coherence terms for associative ionization of two differently excited Na(3p) atoms

The associative ionization process in thermal Na(3p)-Na(3p) encounters has been studied in a series of crossed-beam experiments where the light polarization of the two laser beams preparing the excited atoms before collision was varied independently. It is shown how in this way maximum possible information for our geometry is extracted about the dependence of the ion formation process on the shape and spatial orientation of the electron clouds of the two approaching atoms, including all coherence terms. The experimental findings are discussed in the light of recent theoretical results for the states of the Na2 molecule. It is concluded that just a few of the possible geometrical approaches are favourable for molecular-ion formation. (orig.)