Multiphoton ionization of neat liquid D2O 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 D2O. 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.

With the help of Monte Carlo simulation techniques, we study the recombination kinetics of hydrated electrons (e−aq) with H3O+ and OH⋅ which results from the photoionization of pure water with femtosecond pulsed lasers. A full description of the simulation procedure is given and various comparisons are made with analytical formulations of the reaction kinetics. Particular attention is given to the reaction of e−aq with H3O+, which is only partially diffusion controlled and which involves a Coulombic interaction with dielectric saturation effects. We find that the probability of reaction per e−aq –H3O+ encounter is small (∼6%) and that the encounter duration can be of the order of a few picoseconds. The competition between the reaction of e−aq with H3O+ and with OH⋅ is analyzed with the simulations and with the independent reaction times method. Both approaches indicate that the e−aq decay is largely dominated by the reaction of e−aq with OH⋅. The effect of neighboring ionization sites on the e−aq decay kinetics is also included in the simulations to account for different possible densities of ionization sites. The initial separation between the reactants is found to be about 1 nm, in agreement with previous determinations. The significance of this last value and the constraints that it puts on the initial kinetic energy of the photoelectrons is discussed.

Monte Carlo simulations were performed to calculate the temperature dependence of the primary yields (g-values) of the radical and molecular products of the radiolysis of pure, deaerated liquid water by low linear-energy-transfer (LET) radiation. The early energy deposition was approximated by considering short segments (∼100 μm) of 300-MeV proton tracks (corresponding to an average LET of ∼0.3 keV/μm). The subsequent nonhomogeneous chemical evolution of the reactive species formed in these tracks was simulated by using the independent reaction times approximation, which has previously been used successfully to model the radiolysis of liquid water at ambient temperature under various conditions. Our calculated g-values for the radiolytic species:  , OH, H, H2, and H2O2, are presented as a function of temperature over the range 25−300 °C. They show an increase in g( ), g(OH), and [g(H) + g(H2)] and a decrease in g(H2O2) with increasing temperature, in agreement with existing experimental data. The sensitivity of the results to the values of reaction rate constants and to the temperature dependence of electron thermalization distances (r th) was also investigated. It was found that the best agreement with experiment occurs when the distances of electron thermalization decrease with increasing temperature, a result that is at variance with the predictions of previous modeling studies. Such a decrease in r th as the temperature increases could be linked to an increase in the scattering cross sections of subexcitation electrons that would account for the corresponding decrease in the degree of structural order of water molecules. Our simulations also suggest that the variations of the g-values with temperature, and especially that of g(H2), are better described if we account for the screening of the Coulomb forces between the two in the bimolecular self-reaction of the hydrated electron. Finally, the time-dependent yields of and OH are presented as functions of temperature, in the range 10-12−10-6 s. It was found that the temporal variation of g( ) at elevated temperatures is sensitive to the temperature dependence of r th, suggesting that measurements of the decay of hydrated electrons as functions of time and temperature could, in turn, provide information on the thermalization of subexcitation electrons. The good overall accord of our calculated results with the experimental data available from the literature demonstrates that Monte Carlo simulation methods offer a most promising avenue at present to further develop our understanding of temperature effects in the radiolysis of liquid water.

Multiphoton ionization of neat methanol at room temperature (294 K) with 2-eV laser pulses (-300 fs) is used to study electron solvation. For the first time the experimental conditions allowed a quantitative as well as a qualitative study of the formation and evolution of the solvated electron in methanol. The kinetics exhibits a continuous blue shift of the spectral peak. This shift from 1.57 to 1.92 eV is found to be exponential with a characteristic time of 13.6 f 0.6 ps. A simultaneous stepwise process is evidenced by the concurrent first-order (6.1 f 0.6 ps) absorption decay in the infrared and growth in the visible. Our proposed hybrid model of electron solvation involves two electron-solvent configuration states (a weakly bound and a strongly bound one) in both of which relaxation occurs via a continuous shift and between which there is a stepwise transfer mechanism. About 50% of the electrons are found in the strongly bound state within the first picosecond, suggesting that they are trapped directly into this state.

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