The photodissocn. of I2 was studied in the gas phase by laser flash photolysis. The decrease of the quantum yield with increasing C2H5 and C3H8 pressure is interpreted in terms of the cage effect. As the temp. is increased a less pronounced cage effect is obsd. The trends in the measured quantum yields with changing temp. and pressure agree with model calcns. for dissocn. in a viscous continuum. However the simple model applied is not useful for quant. predictions. The 2nd order rate const. for 1 atom recombination increases slightly with increasing temp.