Electronic excited-state mixing in NeCl2.

Ab initio calculations that explicitly include spin-orbit interactions are reported for the NeCl2 system of electronic states. A surprising curve crossing is observed for the C2v, T-shaped geometry. Away from the C2v geometry, the states mix, as expected. On the basis of these new results we propose a new mechanism for electronic energy transfer from highly vibrationally excited levels of the B electronic state of the chlorine molecule. It is proposed that as long as vibrational predissociation of NeCl2 proceeds by direct coupling of the initial state to the continuum states the Ne atom does not sample geometries that efficiently quench the Cl2 B electronic state. However, when the vibrational dynamics changes to the intramolecular vibrational relaxation regime the Ne atom becomes quite effective at coupling the Cl2 B3Pi0u+ state with a 3Pi2g state.