Cage effect for the abstraction of H from H2O in Ar matrices

Abstract

A red wing in the absorption of H₂O in the first continuum which extends beyond 200 nm is induced by the matrix. A threshold energy of 6.95 eV is found for the quantum efficiency of permanent dissociation of H₂O into OH and H. This corresponds to an additional barrier of 1.8 eV due to the matrix cage. The barrier is attributed to the sum of repulsive H–Ar pair potentials in an interstitial site of D₃ symmetry, which has to be surmounted by the H atom on the way from the initial substitutional H₂O site to the final stable O_h site of the abstracted H atom.