Thermodynamic changes associated with the formation of the hydrated electron after photoionization of inorganic anions: a time-resolved photoacoustic study

Borsarelli, Claudio D.; Bertolotti, Sonia G.; Previtali, Carlos M.

doi:10.1039/b302050a

Cited by 29 publications

(20 citation statements)

References 30 publications

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“…[19][20][21][22][23][24] Indeed, our potential, dubbed Larsen-Glover-Schwartz (LGS) in the literature, predicts that the electron is overly bound energetically 19,20,25 and has a negative molar volume of solvation, 26 in contrast to what is known from experiment. 27,28 On the other hand, our non-cavity picture provides many qualitatively and even quantitatively correct predictions that are missed by the more standard cavity model, including the shape of the O-H stretching band in the hydrated electron's resonance Raman spectrum, 16,17 the temperaturedependence of the electron's ground-state absorption spectrum, 16,17 the hydrated electron's time-resolved photoelectron spectroscopy, 29 and the behavior of hydrated electrons at the air/water interface. 26 Other recent theoretical calculations, which suggest a "hybrid" model with an electron that has only a small central cavity, still require a significant electronwater overlap like that in our non-cavity model to reproduce experimental findings.…”

Section: Introductionmentioning

confidence: 77%

Temperature dependence of the hydrated electron’s excited-state relaxation. II. Elucidating the relaxation mechanism through ultrafast transient absorption and stimulated emission spectroscopy

Farr

Zho

Challa

et al. 2017

The Journal of Chemical Physics

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The structure of the hydrated electron, particularly whether it exists primarily within a cavity or encompasses interior water molecules, has been the subject of much recent debate. In Paper I [C.-C. Zho et al., J. Chem. Phys. 147, 074503 (2017)], we found that mixed quantum/classical simulations with cavity and non-cavity pseudopotentials gave different predictions for the temperature dependence of the rate of the photoexcited hydrated electron's relaxation back to the ground state. In this paper, we measure the ultrafast transient absorption spectroscopy of the photoexcited hydrated electron as a function of temperature to confront the predictions of our simulations. The ultrafast spectroscopy clearly shows faster relaxation dynamics at higher temperatures. In particular, the transient absorption data show a clear excess bleach beyond that of the equilibrium hydrated electron's ground-state absorption that can only be explained by stimulated emission. This stimulated emission component, which is consistent with the experimentally known fluorescence spectrum of the hydrated electron, decreases in both amplitude and lifetime as the temperature is increased. We use a kinetic model to globally fit the temperature-dependent transient absorption data at multiple temperatures ranging from 0 to 45 C. We find the room-temperature lifetime of the excited-state hydrated electron to be 137±40 fs, in close agreement with recent time-resolved photoelectron spectroscopy (TRPES) experiments and in strong support of the "non-adiabatic" picture of the hydrated electron's excited-state relaxation. Moreover, we find that the excited-state lifetime is strongly temperature dependent, changing by slightly more than a factor of two over the 45C temperature range explored. This temperature dependence of the lifetime, along with a faster rate of ground-state cooling with increasing bulk temperature, should be directly observable by future TRPES experiments. Our data also suggest that the red side of the hydrated electron's fluorescence spectrum should significantly decrease with increasing temperature. Overall, our results are not consistent with the nearly complete lack of temperature dependence predicted by traditional cavity models of the hydrated electron but instead agree qualitatively and nearly quantitatively with the temperature-dependent structural changes predicted by the non-cavity hydrated electron model.

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Section: Introductionmentioning

confidence: 77%

Temperature dependence of the hydrated electron’s excited-state relaxation. II. Elucidating the relaxation mechanism through ultrafast transient absorption and stimulated emission spectroscopy

Farr

Zho

Challa

et al. 2017

The Journal of Chemical Physics

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“…The solid line in the figure is the prediction from the Stokes–Einstein–Debye (SED) equation: 1 τ calc normalr = 6 D SED = k normalB T V η ( 3 2 ρ false[ ( 2 ρ 2 − 1 ) S − ρ false] ρ 4 − 1 ) S = false( ρ 2 − 1 false) − 1 / 2 .25em ln [ ρ + ( ρ 2 − 1 ) 1 / 2 ] where V and ρ are the solute volume and the axial ratio of solute, respectively. These parameters were taken from the literature (0.04 nm 3 and 1.89 for V and ρ, respectively ,, ). As is shown in the figure, the relaxation times in RTILs are shorter than the prediction from the SED theory.…”

Section: Resultsmentioning

confidence: 99%

Ultrafast Relaxation and Reaction of Diiodide Anion after Photodissociation of Triiodide in Room-Temperature Ionic Liquids

2012

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Vibrational dephasing, vibrational relaxation, and rotational relaxation of diiodide (I(2)(-)) after photodissociation of triiodide (I(3)(-)) in room-temperature ionic liquids (RTILs) were investigated by ultrafast transient absorption spectroscopy. The vibrational energy relaxation (VER) rate of I(2)(-) produced by the photodissociation reaction of I(3)(-) was determined from the spectral profile of the transient absorption. The rates in RTILs were slightly slower than those in conventional liquids. On the other hand, the coherent vibration of I(2)(-) was not observed in RTILs, and the vibrational dephasing of the photoproduced I(2)(-) was accelerated. This was explained by the interaction between I(2)(-) and I consisting of a caged contact pair in RTILs. The orientational relaxation time of I(2)(-) determined by the transient absorption anisotropy was much longer in RTILs than in conventional liquids due to their high viscosities although the relaxation time was shorter than the prediction from the Stokes-Einstein-Debye (SED) theory. The deviation from the SED prediction was interpreted by the frequency dependence of the shear stress acting on the molecule. The dynamics of I(2)(-) in 1-butyl-3-methylimidazolium iodide ([BMIm]I) were quite different from those in other conventional RTILs: the coherent vibration of I(2)(-) was observed for the time profile of the transient absorption and the initial value of the anisotropy was reduced to 0.31 from 0.36 in conventional RTILs. These results suggest that an ultrafast reaction between the photofragment I and the solvent I(-) may occur during the photodissociation process of I(3)(-). The anomaly in the ground state coherent vibration and steady state Raman spectrum of I(3)(-) also suggest the possibility that I(3)(-) and I(-) can be located in vicinity and interact strongly with each other in [BMIm]I.

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“…We note that our one-electron non-cavity pseudopotential has been criticized, [24][25][26] both for overbinding the electron energetically 15,27 and for predicting a negative molar solvation volume 28 when experiment suggests that this parameter should be positive. 29 Nevertheless, non-cavity hydrated electron models have been shown to account for 0021-9606/2017/147(7)/074503/14/$30.00…”

Section: Introductionmentioning

confidence: 99%

Temperature dependence of the hydrated electron’s excited-state relaxation. I. Simulation predictions of resonance Raman and pump-probe transient absorption spectra of cavity and non-cavity models

Zho

Farr

Glover

et al. 2017

The Journal of Chemical Physics

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We use one-electron non-adiabatic mixed quantum/classical simulations to explore the temperature dependence of both the ground-state structure and the excited-state relaxation dynamics of the hydrated electron. We compare the results for both the traditional cavity picture and a more recent non-cavity model of the hydrated electron and make definite predictions for distinguishing between the different possible structural models in future experiments. We find that the traditional cavity model shows no temperature-dependent change in structure at constant density, leading to a predicted resonance Raman spectrum that is essentially temperature-independent. In contrast, the non-cavity model predicts a blue-shift in the hydrated electron's resonance Raman O-H stretch with increasing temperature. The lack of a temperature-dependent ground-state structural change of the cavity model also leads to a prediction of little change with temperature of both the excited-state lifetime and hot ground-state cooling time of the hydrated electron following photoexcitation. This is in sharp contrast to the predictions of the non-cavity model, where both the excited-state lifetime and hot ground-state cooling time are expected to decrease significantly with increasing temperature. These simulation-based predictions should be directly testable by the results of future time-resolved photoelectron spectroscopy experiments. Finally, the temperature-dependent differences in predicted excited-state lifetime and hot ground-state cooling time of the two models also lead to different predicted pump-probe transient absorption spectroscopy of the hydrated electron as a function of temperature. We perform such experiments and describe them in Paper II [E. P. Farr et al., J. Chem. Phys. 147, 074504 (2017)], and find changes in the excited-state lifetime and hot ground-state cooling time with temperature that match well with the predictions of the non-cavity model. In particular, the experiments reveal stimulated emission from the excited state with an amplitude and lifetime that decreases with increasing temperature, a result in contrast to the lack of stimulated emission predicted by the cavity model but in good agreement with the non-cavity model. Overall, until ab initio calculations describing the non-adiabatic excited-state dynamics of an excess electron with hundreds of water molecules at a variety of temperatures become computationally feasible, the simulations presented here provide a definitive route for connecting the predictions of cavity and non-cavity models of the hydrated electron with future experiments.

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Thermodynamic changes associated with the formation of the hydrated electron after photoionization of inorganic anions: a time-resolved photoacoustic study

Cited by 29 publications

References 30 publications

Temperature dependence of the hydrated electron’s excited-state relaxation. II. Elucidating the relaxation mechanism through ultrafast transient absorption and stimulated emission spectroscopy

Temperature dependence of the hydrated electron’s excited-state relaxation. II. Elucidating the relaxation mechanism through ultrafast transient absorption and stimulated emission spectroscopy

Ultrafast Relaxation and Reaction of Diiodide Anion after Photodissociation of Triiodide in Room-Temperature Ionic Liquids

Temperature dependence of the hydrated electron’s excited-state relaxation. I. Simulation predictions of resonance Raman and pump-probe transient absorption spectra of cavity and non-cavity models

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