EFFECT OF PRESSURE ON MOLECULAR PHOTODISSOCIATION IN MATRICES - MOLECULAR-DYNAMICS SIMULATIONS OF CL2 IN XE

A theoretical study is presented on the photodissociation dynamics of Cl2 in crystalline xenon at 100 K, and within a range of pressure between 0 and 100 kbar. Temperature/pressure ensemble molecular dynamics simulations were carried out. The potentials used were accurate enough to reproduce the experimental equation of state of solid xenon. The results show that the photodissociation quantum yield varies strongly with pressure, falling from 30% at zero pressure, to 2% at 12.5 kbar, and 0% at higher pressures. These yields are in good agreement with experimental measurements. This behavior is found to be due to the strong effect of pressure on the librational (rotational) amplitudes of the Cl2 molecule and to the sharp dependence of the photodissociation yield on the molecular orientation in the reagent cage.