Photochemistry in Van Der Waals Complexes: (Hg—H2)* → HgH + H

The Hg—H 2 collision complex in the reaction Hg 3 P 1 + H 2 has been investigated by anew method involving the Van der Waals complex of the reactants. This method yieldsthe first observation of a vibrational transition in a reactive collision complex. Furthermorethe fixed geometry of the Van der Waals complex corresponding to the Hg 3 P 1 state enables the separation of two different reaction paths depending on the electronicconfiguration of the complex, namely Σ 3 and Π 3 .