PHOTODISSOCIATION OF WATER IN RARE-GAS MATRICES - CAGE EFFECT AND LOCAL HEATING OF THE LATTICE

The H fragment produced in the photodissociation of water (H2O --> H + OH) is lighter than the lattice atoms and a local heating occurs over long time scales and large spatial regions. Therefore, use of a continuum model for the lattice is justified. The local heating is promoted by a decreasing heat conductivity with increasing temperature. Solutions of a nonlinear heat conductivity equation show that the heat release inside the cage leads to a temperature increase in its nearest surroundings up to the melting point in argon. Melting enables the light fragment to overcome the cage barrier. In the case of krypton, the thermal effect is less pronounced, while in Xe, there is none. The above results are in qualitative agreement with experimental data.