Photodissociation and vibrational relaxation of I2− in ethanol

The dissociation, internal conversion, and vibrational relaxation of photoexcited I2− in ethanol have been examined using ultrafast transient-absorption spectroscopy. I2− was photoexcited at 770 nm (1.6 eV) and probed on the subpicosecond time scale at 15 wavelengths between 580 and 950 nm, permitting a determination of the temporal evolution of the absorption spectrum. The data reveal that internal conversion and vibrational relaxation at the top of the well are extremely rapid (≤0.3 ps), with loss of the final 0.3 eV of energy (v≤20) occurring on a time scale of ∼4 ps. Simple kinetic and spectral models are able to qualitatively account for the observed behavior of the transient-absorption signals.