Photodissociation and recombination dynamics of I<SUB>2</SUB> in DDR (decadodecasil 3R): Dependence on the geometry of the host matrix monitored by femtosecond time-resolved pump–probe experiments

We present polarization dependent femtosecond time-resolved pump–probe experiments on iodine molecules embedded in well-defined cages of the crystalline microporous SiO₂ modification decadodecasil 3R (DDR). Inside the DDR porosils the I₂ molecules reside isolated from each other in hexagonal cages of ≈350 ų. After pump excitation of the B 0<stack><above>+</above><below>u</below></stack> (³Π) state, the collision induced dissociation takes place via different crossing repulsive potential curves. The surrounding cages cause the atoms to recombine. The resulting iodine molecules are prepared in their A, A', and X states where vibrational relaxation takes place due to the collisions with the surroundings. For a better understanding of the complex dynamics, a theoretical model was developed based on the classical Langevin equation (Brownian dynamics). The simulations of the experimental data obtained from powder samples are compared with earlier calculations by Ermoshin et al. (V. A. Ermoshin, G. Flachenecker, A. Materny and V. Engel, J. Chem. Phys., 2001, 114, 8132) based on molecular dynamics modeling. Brownian dynamics simulations are also applied to polarization dependent pump–probe experiments on single crystalline I₂-DDR samples. It is demonstrated, that by switching the polarization of the lasers relative to the crystal axis the predissociation process of the excited B state of I₂ can be influenced. This effect can be simulated using the theoretical model.