Isotopic dependence of recombination kinetics in water

Chernovitz, Anita C.; Jonah, Charles D.

doi:10.1021/j100332a021

Cited by 66 publications

(50 citation statements)

References 3 publications

(4 reference statements)

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“…[54][55][56] Even for direct ionization, which is the only mechanism where nuclear motion does not play a primary role in the ionization process, different inelastic scattering efficiencies are likely to give an isotope dependence of the ejection length. As we discuss below, different energy loss rates for inelastic scattering of an electron in the two liquids have been implicated in the different geminate kinetics following radiolysis, [56][57][58] although the radiolysis result seems to contrast with our observations following two-photon excitation in the range of 8.3-12.4 eV.…”

Section: Isotope Dependence Of the Ejection Lengthmentioning

confidence: 99%

“…[56][57][58] A common interpretation of that observation is that electrons travel further in D 2 O, because the stretching and bending vibrational frequencies are lower in D 2 O than in H 2 O and inelastic scattering from the lower energy vibrations is less efficient at dissipating kinetic energy from the electron. 56 Gas phase electron-scattering measurements confirm that the cross section for vibrational excitation of isolated D 2 O is smaller than for H 2 O, 64 supporting the conclusion that more collisions with D 2 O than H 2 O are necessary to remove the same amount of kinetic energy from an electron. The rate of energy dissipation is often related to the dielectric response of the liquid as well, suggesting that even electrons with kinetic energy below the vibrational levels of water travel further in D 2 O, which has a longer dielectric relaxation time than H 2 O.…”

Section: Isotope Dependence Of the Ejection Lengthmentioning

confidence: 99%

See 1 more Smart Citation

Excitation-energy dependence of the mechanism for two-photon ionization of liquid H2O and D2O from 8.3to12.4eV

Elles

Jailaubekov

Crowell

et al. 2006

The Journal of Chemical Physics

119

192

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Transient absorption measurements monitor the geminate recombination kinetics of solvated electrons following two-photon ionization of liquid water at several excitation energies in the range from 8.3 to 12.4 eV. Modeling the kinetics of the electron reveals its average ejection length from the hydronium ion and hydroxyl radical counterparts and thus provides insight into the ionization mechanism. The electron ejection length increases monotonically from roughly 0.9 nm at 8.3 eV to nearly 4 nm at 12.4 eV, with the increase taking place most rapidly above 9.5 eV. We connect our results with recent advances in the understanding of the electronic structure of liquid water and discuss the nature of the ionization mechanism as a function of excitation energy. The isotope dependence of the electron ejection length provides additional information about the ionization mechanism. The electron ejection length has a similar energy dependence for two-photon ionization of liquid D 2 O, but is consistently shorter than in H 2 O by about 0.3 nm across the wide range of excitation energies studied.

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Section: Isotope Dependence Of the Ejection Lengthmentioning

confidence: 99%

Section: Isotope Dependence Of the Ejection Lengthmentioning

confidence: 99%

Excitation-energy dependence of the mechanism for two-photon ionization of liquid H2O and D2O from 8.3to12.4eV

Elles

Jailaubekov

Crowell

et al. 2006

The Journal of Chemical Physics

119

192

View full text Add to dashboard Cite

show abstract

“…Nevertheless, recent experiments which probe the presence of the excited state electron more directly via selective scavengers 12,13,14 appear to rule out such a short lifetime, consistent with classic work along these lines. 15 These papers place the lifetime at ~300-500 fs. The different possible mechanistic models point to the ambiguity of the interpretation of the experimental signals.…”

Section: Introductionmentioning

confidence: 99%

Nuclear quantum effects on the nonadiabatic decay mechanism of an excited hydrated electron

Borgis¹,

Rossky²,

Túri³

2007

The Journal of Chemical Physics

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We present a kinetic analysis of the non-adiabatic decay mechanism of an excited state hydrated electron to the ground state. The theoretical treatment is based on a quantized, gap dependent golden rule rate constant formula which describes the non-adiabatic transition rate between two quantum states. The rate formula is expressed in terms of quantum time correlation functions of the energy gap, and of the non-adiabatic coupling. These gap dependent quantities are evaluated from three different sets of mixed quantum-classical molecular dynamics simulations of a hydrated electron equilibrated a) in its ground state, b) in its first excited state, and c) on a hypothetical mixed potential energy surface which is the average of the ground and the first excited electronic states. The quantized, gap-dependent rate results are applied in a phenomenological kinetic equation which provides the survival probability function of the excited state electron. Although the lifetime of the equilibrated excited state electron is computed to be very short (well under 100 fs), the survival probability function for the non-equilibrium process in pump-probe experiments yields an effective d

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“…[31] Laenen et al [29] have shown clear evidence for the existence of consecutive e pre À states with lifetimes of 110 fs, 200 fs, and 540 fs, which have absorption peaks at 2900 nm, 1600 nm, and approximately 900 nm, respectively, following twooton excitation of H 2 O. Moreover, a number of previous studies [32][33][34] have obtained interesting results about the ET reactions of e pre À with conventional electron scavengers, mainly by studying the formation and decay kinetics of the hydrated electron and the e hyd À yield. However, real-time observation of the transition state of an e pre À -scavenger reaction was only obtained recently.…”

mentioning

confidence: 96%

Real‐Time Observation of a Molecular Reaction Mechanism of Aqueous 5‐Halo‐2′‐deoxyuridines under UV/Ionizing Radiation

Wang

2007

Angew Chem Int Ed

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Electron transfer (ET) underlies many processes in molecular systems of chemical, biological, and environmental significance and is therefore a subject of continued interest. [1][2][3][4][5][6] Real-time observation of the transition state in an ET reaction may lead to the prediction, understanding, and modification of the course of the reaction. Among available techniques, time-resolved femtosecond (1 fs = 10 À15 s) laser spectroscopy is the most powerful technique for direct observation of the transition states of chemical reactions. [7,8] In particular, this technique is suitable for studying ultrafast electron transfer (UET) reactions in chemical and biological systems. [2,9,10] 5-Halo-2'-deoxyuridines (XdUs, X = Cl, Br, and I), such as bromodeoxyuridine (BrdU) and iododeoxyuridine (IdU), are potential radiosensitizing agents. Replacement of thymidine in DNA by BrdU or IdU has long been known to enhance DNA damage and cell death induced by ionizing radiolysis and UV photolysis. [11][12][13][14] In addition, BrdU and IdU have also been employed to probe protein-nucleic acid interactions by inducing DNA/RNA-protein photocross-linking.[15] As potential sensitizers for radiotherapy of cancer, BrdU and IdU have been tested in several Phase I-III clinical trials.[16] However, the clinical results were not satisfactory, and therefore no XdUs have been approved for clinical use. This may be related to the fact that the mechanism of the radiosensitivity enhancement is not well understood. In the action of halouracils (XUs) it was believed that the first and critical step is the dissociative attachment (DA) of a radiation-generated hydrated electron (e hyd À ) to an aqueous XU, leading to the formation of an anion and a highly reactive radical UC : e hyd À + XU!XU* À !X À + UC . [17,18] This seems reasonable as gaseous halogenated molecules, such as XUs and BrdU, generally have very large cross sections for DA to near 0-eV electrons. [19][20][21] For the reactions of electrons with XUs in water, Rivera and Schuler [17] successfully observed the formation of anionic XU À states that have a transient absorption peak at 330 nm in their nanosecond pulse radiolysis experiments. The XU À absorption at approximately 330 nm slightly red-shifts from the absorption at 280-290 nm of their parent neutral XUs. In gas-phase experiments, Abdoul-Carime et al. [20] showed that the efficiency for the uracil-5-yl radical formation by DA of nearly 0-eV electrons is in the order of BrU > ClU > IU, whereas the efficiency for the halogen atomic radical is ClU > BrU > IU. They thus concluded that ClU should be the most effective radiosensitizer among halouracils. This conclusion seems inconsistent with the observations of the biological and therapeutic effects of XdUs, which have so far shown effective radiosensitization by IdU and BrdU only [11][12][13][14][15][16] and with the theoretical calculations by Li et al. [22] that have showed the DA efficiency of BrU = ClU @ FU to low-energy electrons.By using time-resolved femtosecond (fs) laser ...

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Isotopic dependence of recombination kinetics in water

Cited by 66 publications

References 3 publications

Excitation-energy dependence of the mechanism for two-photon ionization of liquid H2O and D2O from 8.3to12.4eV

Excitation-energy dependence of the mechanism for two-photon ionization of liquid H2O and D2O from 8.3to12.4eV

Nuclear quantum effects on the nonadiabatic decay mechanism of an excited hydrated electron

Real‐Time Observation of a Molecular Reaction Mechanism of Aqueous 5‐Halo‐2′‐deoxyuridines under UV/Ionizing Radiation

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