Cage effect for the photodissociation of H2O molecules in argon clusters embedded inside neon clusters

A study of energy relaxation processes of H2O-doped rare gas clusters excited with vacuum ultraviolet synchrotron radiation is presented. An enhanced quenching of electronically excited fragment OH*(A) is observed in ArmNeN clusters (m<10(2), N≈7.5x10(3)). The doping of interior of small argon clusters has been achieved by using a sequential pick-up technique (Ne-N+H2O+mAr). Due to a low temperature of the Ne host cluster the Ar atoms are fixed around the H2O molecule prohibiting structural rearrangements. A strong decrease of the OH*(A) fluorescence yield has been observed for m>m(1)=12. This effect is attributed to a formation of the second (m(2)=54) and higher shells of Ar atoms around the water molecule. The principal contribution from a noncomplete second shell (m(2)*=32) after a closure of 20 triangular windows in the first shell is suggested. Due to a finite size of the cluster matrix and fast sample renewal, the cage exit and reentry processes can be investigated. (C) 2002 American Institute of Physics.