Iodine solvent-induced dissociation

The use of wavepacket spectroscopy to follow the solvent-induced dissociation of iodine in solution has been described in detail by Scherer, Jonas, and co-workers [18, 28, 30]. Recently the role of the solvent in inducing the curve crossing has been examined by simulation [29], Remarkably, the experiments show that the wavepacket survives the solvent-induced curve crossing and appears intact (i.e., the atoms are separating ballistically) up to at least 4 A separation [28], The simulations imply that destruction of the wavepacket by the solvent cage (polarizable Ar atoms in this case) occurs between I-I separation of 5-6 A [29]. 

In solution when iodine is excited to the bound B excited state, dissociation and recombination processes occur. The dissociation is the result of solvent-induced curve crossing to the dissociative a state, the recombination a result of momentum reversals arising from collisions with the surrounding solvent molecules. Eigenstates of the B state will decay in a continuous manner, whereas wavepackets—if the curve-crossing probability is less than unity—decay in a stepwise manner, giving rise to successive pulses of product. The B and a curves cross near the center of the B state, whereas the B state wavepacket is initially created near the left turning point thus there... 

Collision-induced vibrational excitation and relaxation by the bath molecules are the fundamental processes that characterize dissociation and recombination at low bath densities. The close relationship between the frequency-dep>endent friction and vibrational relaxation is discussed in Section V A. The frequency-dependent collisional friction of Section III C is used to estimate the average energy transfer jjer collision, and this is compared with the results from one-dimensional simulations for the Morse potential in Section V B. A comparison with molecular dynamics simulations of iodine in thermal equilibrium with a bath of argon atoms is carried out in Section V C. The nonequilibrium situation of a diatomic poised near the dissociation limit is studied in Section VD where comparisons of the stochastic model with molecular dynamics simulations of bromine in argon are made. The role of solvent packing and hydrodynamic contributions to vibrational relaxation are also studied in this section. 

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