Recombination dynamics of photodissociated I2− in size selected Ar and CO2 clusters

We report time-resolved photodissociation and geminate recombination dynamics of I2− in size-selected I2− Arn and I2−(CO2)n cluster ions by using ultrafast pump–probe techniques at 790 nm in conjunction with a tandem time-of-flight mass spectrometer. The absorption recovery, which reflects the time scale for photodissociation followed by recombination and vibrational relaxation of I2− inside the cluster, shows a strong dependence on the composition of the surrounding cluster solvent. The absorption recovery time for I2−(CO2)16 is ∼1 ps, whereas for I2−Ar20 it is ∼130 ps. This difference is discussed in terms of electrostatic and hard sphere interactions. We also observe the time dependence of the destruction of the Ar solvent cage for I2−Ar16. Finally, absorption recovery data for I2−(CO2)n cluster ions taken with 790 nm pump–probe wavelengths are compared with the greater energy release 720 nm data.