Observation of a Continuous Spectral Shift in the Solvation Kinetics of Electrons in Neat Liquid Deuterated Water

Multiphoton ionization of neat liquid D 2 O at room temperature (295 K) with 2-eV subpicosecond laser pulses is used to study the solvation of electrons in this medium. The set of 20 measured kinetic traces covers a wide range of probing wavelengths (450−1450 nm), which allows us to obtain a global picture of the spectral changes that accompany electron hydration. The construction of transient absorption spectra from a proper normalization of the kinetic traces confirms the well-known existence of two absorbing species, one weakly bound absorbing chiefly in the infrared and a strongly bound one whose spectrum at long times is that of the well-characterized hydrated electron. The transient spectra also reveal the occurrence of a stepwise transition between these two species as well as a concomitant continuous blue shift of the strongly bound electron−solvent configuration. A nonlinear fit performed simultaneously on all the data allows the estimation of the characteristic kinetic and spectral parameters of our previously proposed hybrid model of electron solvation when it is applied to D 2 O. The global fit closely matches the data for the 20 different probing wavelengths investigated. The electrons are found to get trapped in 0.16 ± 0.02 ps, whereas the stepwise transition and the continuous blue shift characteristic times are 0.41 ± 0.02 and 0.51 ± 0.03 ps, respectively. The extent in energy of the monoexponential blue shift of the strongly bound electron spectrum is 0.34 ± 0.02 eV, a value which is very similar to the one that was found for electron solvation in methanol. Finally, it is estimated that about 34% of the electrons get directly trapped into the strongly bound state.