Primary processes in the radiation chemistry of water

Jonah, Charles D.; Bartels, David M.; Chernovitz, Anita C.

doi:10.1016/1359-0197(89)90019-2

Cited by 13 publications

(19 citation statements)

References 61 publications

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“…One of the most basic assumptions made in radiation physics and chemistry is that when vertical ionization occurs in (nonconducting) condensed phase systems, the kinetic energy imparted to the electron correlates with the ultimate distance it travels away from its geminate positive ion prior to thermalization and trapping. ,, The distance reached is certainly a highly nonlinear function of the initial energy: almost all of the energy could be dissipated in a single scattering event for initial energies above the first electronic excitation threshold. Once the electron reaches “subexcitation” energies, a large number of energy scattering events may be required to dissipate the energy into vibrational modes, and it is believed that most of the electron travel occurs in this energy regime (on a femtosecond time scale 23 ).…”

Section: Discussionmentioning

confidence: 99%

Multiphoton Ionization of Liquid Water with 3.0−5.0 eV Photons

1996

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We report a picosecond laser study of the transient absorption of hydrated electrons generated by the 3-5 eV multiphoton ionization of liquid water. The geminate kinetics indicate that e aqis produced by at least three different mechanisms over this energy range. Power dependence of the signal amplitude shows a two-photon threshold for 4.0 eV excitation and a three-photon threshold absorption at 3.47 eV, consistent with two-or three-photon excitation of the A ˜(1 B 1 ) lowest excited state. For (three-photon) excitation in the range 3.02-3.47 eV very little (e15%) geminate recombination is observed while for the (two-photon) excitation at shorter wavelengths significant recombination (g55%) is observed. In the region of 3.85-4.54 eV, photonenergy-independent kinetics indicate that e aqis produced via two-photon excitation of the A ˜state followed by an ionization process in which the electrons do not obtain any excess kinetic energy. For photon energies in the range of 4.75-5.05 eV, the escape fraction increases slightly, consistent with two-photon excitation of higher energy states. Simulation with a diffusion model shows that the electron is ejected at least 25 Å farther into the bulk for the 3.02-3.47 eV photon energies relative to two-photon ionization in the 3.67-5.0 eV range. We conclude that the larger distances result from a (3 + 1)-photon resonance-enhanced multiphoton ionization (REMPI) process, made possible by visible/near-UV absorption of the water excited states. Possible mechanisms of the water ionization are discussed. A new mechanism is proposed to explain the production of solvated electrons from excitation of the A ˜(1 B 1 ) state of liquid water, well below the Born-Oppenheimer ionization threshold. On the basis of the gas phase properties of this state, we assume a direct dissociation to give OH radical and H atoms, with the excess energy almost entirely transferred to kinetic energy of the H atoms: H 2 O* f OH + H(hot). It is proposed that the hot H atoms immediately react with an adjacent water molecule to form hydronium ion and a solvated electron, in a process analogous to the thermal reaction of H atoms with water at elevated temperatures: H(hot) + H 2 O f H 3 O + + e aq -.

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Section: Discussionmentioning

confidence: 99%

Multiphoton Ionization of Liquid Water with 3.0−5.0 eV Photons

1996

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“…The C 37 parameter is believed to reflect the reactions with electrons before solvation. [134][135][136][137][138][139][140][141] In THF, presolvated states such as an excited state of solvated electrons have not been reported. Therefore, C 37 in THF is likely to be related to the reaction with thermalized and possibly epithermal electrons.…”

Section: )mentioning

confidence: 99%

Radiation Chemistry in Chemically Amplified Resists

Kozawa

Tagawa

2010

Jpn. J. Appl. Phys.

331

319

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Historically, in the mass production of semiconductor devices, exposure tools have been repeatedly replaced with those with a shorter wavelength to meet the resolution requirements projected in the International Technology Roadmap for Semiconductors issued by the Semiconductor Industry Association. After ArF immersion lithography, extreme ultraviolet (EUV; 92.5 eV) radiation is expected to be used as an exposure tool for the mass production at or below the 22 nm technology node. If realized, 92.5 eV EUV will be the first ionizing radiation used for the mass production of semiconductor devices. In EUV lithography, chemically amplified resists, which have been the standard resists for mass production since the use of KrF lithography, will be used to meet the sensitivity requirement. Above the ionization energy of resist materials, the fundamental science of imaging, however, changes from photochemistry to radiation chemistry. In this paper, we review the radiation chemistry of materials related to chemically amplified resists. The imaging mechanisms from energy deposition to proton migration in resist materials are discussed.

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“…11 Therefore, numerous kinetic studies have been devoted to elucidating the rates of processes induced by water ionization. 12 At ultrafast times and at the molecular level, unlike for the solvated electron product, the information about the chemical dynamics of the cationic hole leading to formation of OH is not so clear and subject to far fewer investigations. 8,9 It is usually assumed that the proton transfer reaction happens faster than 100 fs and this value is given in nearly all introductory texts on radiation damage of water and biological tissues.…”

Section: Introductionmentioning

confidence: 99%

Chasing charge localization and chemical reactivity following photoionization in liquid water

Maršálek

Elles

Pieniazek

et al. 2011

The Journal of Chemical Physics

105

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The ultrafast dynamics of the cationic hole formed in bulk liquid water following ionization is investigated by ab initio molecular dynamics simulations and an experimentally accessible signature is suggested that might be tracked by femtosecond pump-probe spectroscopy. This is one of the fastest fundamental processes occurring in radiation-induced chemistry in aqueous systems and biological tissue. However, unlike the excess electron formed in the same process, the nature and time evolution of the cationic hole has been hitherto little studied. Simulations show that an initially partially delocalized cationic hole localizes within ∼30 fs after which proton transfer to a neighboring water molecule proceeds practically immediately, leading to the formation of the OH radical and the hydronium cation in a reaction which can be formally written as H 2 O + + H 2 O → OH + H 3 O + . The exact amount of initial spin delocalization is, however, somewhat method dependent, being realistically described by approximate density functional theory methods corrected for the self-interaction error. Localization, and then the evolving separation of spin and charge, changes the electronic structure of the radical center. This is manifested in the spectrum of electronic excitations which is calculated for the ensemble of ab initio molecular dynamics trajectories using a quantum mechanics/molecular mechanics (QM/MM) formalism applying the equation of motion coupled-clusters method to the radical core. A clear spectroscopic signature is predicted by the theoretical model: as the hole transforms into a hydroxyl radical, a transient electronic absorption in the visible shifts to the blue, growing toward the near ultraviolet. Experimental evidence for this primary radiation-induced process is sought using femtosecond photoionization of liquid water excited with two photons at 11 eV. Transient absorption measurements carried out with ∼40 fs time resolution and broadband spectral probing across the near-UV and visible are presented and direct comparisons with the theoretical simulations are made. Within the sensitivity and time resolution of the current measurement, a matching spectral signature is not detected. This result is used to place an upper limit on the absorption strength and/or lifetime of the localized H 2 O + (aq) species.

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Primary processes in the radiation chemistry of water

Cited by 13 publications

References 61 publications

Multiphoton Ionization of Liquid Water with 3.0−5.0 eV Photons

Multiphoton Ionization of Liquid Water with 3.0−5.0 eV Photons

Radiation Chemistry in Chemically Amplified Resists

Chasing charge localization and chemical reactivity following photoionization in liquid water

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