Photochemical and photophysical dynamics of I2 isolated in a rare gas cage

The photochemical and photophysical properties of I2 in Ar, Kr, and Xe matrices have been investigated and are reported here. Following laser excitation high into the B 3π(0+u) and 1πlu dissociative states, prompt emission is observed from the B 3π(0+u), A 3π1u, and A′ 3π2u electronic states depending on the matrix host. In all matrices the emission attributed to the B electronic state lies 200 nm to the red of the excitation wavelength and is generally featureless. The time resolved emission for this state has a detector limited rise and fall. The emission attributed to the A 3πlu electronic state was resolved with a monochromator and the source determined to be the v′=0 level of the A state. The lifetime for this emission is 260 μs and was found to be roughly the same in all matrices. Emission from the A′ 3π2u state was also detected but only in Xe matrices. The measured lifetime for this state was 6.3 ms. Data from a number of previous experiments on matrix isolated halogens in Ar, Kr, and Xe are reviewed and a consistent model for the relaxation pathways for intramolecular electronic energy transfer is presented. The implications of this model for studies of the solvent cage effect on I2 photodissociation and the development of the I2 chemical laser are also discussed.