Iodine vibrational relaxation time

The vibrational relaxation of the B, A, A, and X states is mainly caused by the collisions with the surroundings and was found to be completed after less than 2 ps for room temperature. The strong influence of the surroundings on this process could be demonstrated by polarization dependent measurements on iodine embedded in single crystals of the DDR porosil. At room temperature the relaxation time was found to be longer than 4 ps for iodine molecules oriented parallel to the crystal c axis. 

The decay of the B state population due to predissociation is linked to the dynamics of the vibrational relaxation. It could be shown that a longer relaxation time also resulted in a delayed predissociation of the B state iodine molecules. As soon as the vibrational relaxation is completed, the predissociation is solely determined by the coupling strength between the bound B and the repulsive a/a1 states. The coupling of these states is again a function of the interaction with the surrounding cage. 

Kelley and Rentzepis [297] have recently studied the recombination of iodine atoms in liquid and fluid xenon over times to 150 ps after photolysis. The iodine molecule can be biphotonically dissociated through the state to produce geminate pairs with larger initial separations. Some degree of spin relaxation of excited iodine atoms ( Pi/2) produced by biphotonic excitation may occur and reduce the probability of recombination. There is also evidence that the 11 state of I2 may be collisionally predissociated and that recombination may be more rapid than the rate of vibrational relaxation of the excited 12 state in polyatomic solvents (see also ref. 57). Despite these complications, several workers have attempted to model the time dependence of the recombination (or survival) probability of iodine atom reactions. The simple diffusion equation analysis of recombination probabilities [eqn. 

---