Dynamic Solvation Effects in I^-_2(CO_2)_n Impact onto Solid Surface : Wedge and Cage Effects

Novel mechanisms were found to operate in dissociation of I^-_2 embedded in a CO_2 cluster, I^-_2(CO_2)_n, by its impact onto a silicon surface. The bond of I^-_2 is split by a CO_2 molecule located halfway between the two iodine atoms in the parent I^-_2(CO_2)_n, as if the CO_2 molecule behaves as a molecular \u27wedge\u27 (wedge effect). On the other hand, the dissociation of I^-_2 is suppressed when it is caged in a complete CO_2 molecular shell (cage effect). The wedge effect was also demonstrated by a molecular-dynamics simulation. By measuring the surface-parallel component of the translational energy of the I^-_2 and I^- product anions, it was concluded that a \u27quasi-equilibrium\u27 was established on the surface before the product anions leave from it. The translational-energy distribution of the product anions also shows the cage effect