The water dimer in a too tight matrix cage

When an argon matrix containing hydrogen peroxide dimer is irradiated with 266 nm radiation from a YAG laser, water forms. Some of it is formed as monomer but the main part is formed as dimer. The photogenerated water dimer is formed together with an oxygen molecule in the cage of the parent hydrogen peroxide dimer and the dimer bands are shifted from their normal positions indicating that the cage severely perturbs the product structure.