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Abstract
Electron-induced chemistry is relevant to many processes that occur when ionizing radiation interacts with matter. This includes radiation damage, curing of polymers, and nanofabrication processes but also the formation of complex molecules in molecular ices grown on dust particles in space. High-energy radiation liberates from such materials an abundance of secondary electrons of which most have energies below 20 eV. These electrons efficiently trigger reactions when they attach to molecules or induce electronic excitation and further ionization. This review focuses on the present state of insight regarding the mechanisms of reactions induced by electrons with energies between 0 and 20 eV that lead to formation of larger products in binary ice layers consisting of small molecules (H2O, CO, CH3OH, NH3, CH4, C2H4, CH3CN, C2H6) or some derivatives thereof (C2H5NH2 and (C2H5)2NH, CH2=CHCH3). It summarizes our approach to identify products and quantify their amounts based on thermal desorption spectrometry (TDS) and electron-stimulated desorption (ESD) experiments performed in ultrahigh vacuum (UHV). The overview of the results demonstrates that, although the initial electron-molecule interaction is a non-thermal process, product formation from the resulting reactive species is often governed by subsequent reactions that follow well-known thermal and radical-driven mechanisms of organic chemistry.
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2
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Petrik NG, Kimmel GA. Electron-stimulated reactions in nanoscale water films adsorbed on α-Al2O3(0001). Phys Chem Chem Phys 2018; 20:11634-11642. [DOI: 10.1039/c8cp01284a] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
100 eV electrons are stopped in the H2O portion of the isotopically-layered nanoscale film on α-Al2O3(0001) but D2 is produced at the D2O/alumina interface by mobile electronic excitations and/or hydronium ions.
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Affiliation(s)
- Nikolay G. Petrik
- Physical Sciences Division
- Pacific Northwest National Laboratory
- Richland
- USA
| | - Greg A. Kimmel
- Physical Sciences Division
- Pacific Northwest National Laboratory
- Richland
- USA
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Gadallah KAK, Marchione D, Koehler SPK, McCoustra MRS. Molecular hydrogen production from amorphous solid water during low energy electron irradiation. Phys Chem Chem Phys 2017; 19:3349-3357. [PMID: 28091646 DOI: 10.1039/c6cp06928b] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
This work investigates the production of molecular hydrogen isotopologues (H2, HD, and D2) during low energy electron irradiation of layered and isotopically labelled thin films of amorphous solid water (ASW) in ultrahigh vacuum. Experimentally, the production of these molecules with both irradiation time and incident electron energy in the range 400 to 500 eV is reported as a function of the depth of a buried D2O layer in an H2O film. H2 is produced consistently in all measurements, reflecting the H2O component of the film, though it does exhibit a modest reduction in intensity at the time corresponding to product escape from the buried D2O layer. In contrast, HD and D2 production exhibit peaks at times corresponding to product escape from the buried D2O layer in the composite film. These features broaden the deeper the HD or D2 is formed due to diffusion. A simple random-walk model is presented that can qualitatively explain the appearance profile of these peaks as a function of the incident electron penetration.
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Affiliation(s)
- Kamel A K Gadallah
- School of Engineering and Physical Sciences, Heriot-Watt University, Riccarton, Edinburgh EH14 4AS, UK and Astronomy & Meteorology Department, Faculty of Science, Al-Azhar University, Nasr City, PO Box 11884, Cairo, Egypt.
| | - Demian Marchione
- School of Engineering and Physical Sciences, Heriot-Watt University, Riccarton, Edinburgh EH14 4AS, UK and Science Division, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA
| | - Sven P K Koehler
- School of Chemistry, The University of Manchester, Manchester, M13 9PL, UK and Dalton Cumbrian Facility, The University of Manchester, Westlakes Science & Technology Park, Moor Row, CA24 3HA, UK
| | - Martin R S McCoustra
- School of Engineering and Physical Sciences, Heriot-Watt University, Riccarton, Edinburgh EH14 4AS, UK
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Xu Y, Dibble CJ, Petrik NG, Smith RS, Joly AG, Tonkyn RG, Kay BD, Kimmel GA. A nanosecond pulsed laser heating system for studying liquid and supercooled liquid films in ultrahigh vacuum. J Chem Phys 2017; 144:164201. [PMID: 27131543 DOI: 10.1063/1.4947304] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
A pulsed laser heating system has been developed that enables investigations of the dynamics and kinetics of nanoscale liquid films and liquid/solid interfaces on the nanosecond time scale in ultrahigh vacuum (UHV). Details of the design, implementation, and characterization of a nanosecond pulsed laser system for transiently heating nanoscale films are described. Nanosecond pulses from a Nd:YAG laser are used to rapidly heat thin films of adsorbed water or other volatile materials on a clean, well-characterized Pt(111) crystal in UHV. Heating rates of ∼10(10) K/s for temperature increases of ∼100-200 K are obtained. Subsequent rapid cooling (∼5 × 10(9) K/s) quenches the film, permitting in-situ, post-heating analysis using a variety of surface science techniques. Lateral variations in the laser pulse energy are ∼±2.7% leading to a temperature uncertainty of ∼±4.4 K for a temperature jump of 200 K. Initial experiments with the apparatus demonstrate that crystalline ice films initially held at 90 K can be rapidly transformed into liquid water films with T > 273 K. No discernable recrystallization occurs during the rapid cooling back to cryogenic temperatures. In contrast, amorphous solid water films heated below the melting point rapidly crystallize. The nanosecond pulsed laser heating system can prepare nanoscale liquid and supercooled liquid films that persist for nanoseconds per heat pulse in an UHV environment, enabling experimental studies of a wide range of phenomena in liquids and at liquid/solid interfaces.
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Affiliation(s)
- Yuntao Xu
- Physical Sciences Division, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, USA
| | - Collin J Dibble
- Physical Sciences Division, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, USA
| | - Nikolay G Petrik
- Physical Sciences Division, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, USA
| | - R Scott Smith
- Physical Sciences Division, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, USA
| | - Alan G Joly
- Physical Sciences Division, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, USA
| | - Russell G Tonkyn
- Physical Sciences Division, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, USA
| | - Bruce D Kay
- Physical Sciences Division, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, USA
| | - Greg A Kimmel
- Physical Sciences Division, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, USA
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Zhang R, Bu Y. Bifurcate localization modes of excess electron in aqueous Ca(2+)amide solution revealed by ab initio molecular dynamics simulation: towards hydrated electron versus hydrated amide anion. Phys Chem Chem Phys 2016; 18:18868-79. [PMID: 27351489 DOI: 10.1039/c6cp03552c] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
In this work, we conduct ab initio molecular dynamics simulations on the localization dynamics of an excess electron (EE) in acetamide/Ca(2+) aqueous solutions with three different interaction modes of Ca(2+) with acetamide: tight contact, solvent-shared state, and separated interaction. The simulated results reveal that an EE could exhibit two different localization behaviors in these acetamide/Ca(2+) aqueous solutions depending on different amideCa(2+) interactions featuring different contact distances. For the tight contact and solvent-shared state of amideCa(2+) solutions, vertically injected diffuse EEs follow different mechanisms with different dynamics, forming a cavity-shaped hydrated electron or a hydrated amide anion, respectively. Meanwhile, for the separated state, only one localization pattern of a vertically injected diffuse EE towards the formation of hydrated amide anion is observed. The hindrance of hydrated Ca(2+) and the attraction of the hydrated amide group originating from its polarity and low energy π* orbital are the main driving forces. Additionally, different EE localization modes have different effects on the interaction between the amide group and Ca(2+) in turn. This work provides an important basis for further understanding the mechanisms and dynamics of localizations/transfers of radiation-produced EEs and associated EE-induced lesions and damage to biological species in real biological environments or other aqueous solutions.
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Affiliation(s)
- Ru Zhang
- Institute of Theoretical Chemistry, School of Chemistry and Chemical Engineering, Shandong University, 250100, P. R. China.
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Saenko EV, Feldman VI. Radiation-induced transformations of methanol molecules in low-temperature solids: a matrix isolation study. Phys Chem Chem Phys 2016; 18:32503-32513. [DOI: 10.1039/c6cp06082j] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Radiation-induced transformations of methanol in inert solids at 6 K reveal remarkable matrix effects, and mechanisms and astrochemical implications are discussed.
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Marchione D, Thrower JD, McCoustra MRS. Efficient electron-promoted desorption of benzene from water ice surfaces. Phys Chem Chem Phys 2016; 18:4026-34. [DOI: 10.1039/c5cp06537b] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
We study the desorption of benzene from solid water surfaces during irradiation of ultrathin solid films with low energy electrons.
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Marchione D, McCoustra MRS. Electrons, excitons and hydrogen bonding: electron-promoted desorption from molecular ice surfaces. Phys Chem Chem Phys 2016; 18:29747-29755. [DOI: 10.1039/c6cp05814k] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Desorption of benzene from methanol and diethyl ether ices during irradiation with 250 eV electrons is reported and compared with our previous work on benzene/water ices to highlight the role of hydrogen bonding in excitation transport.
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Jensen ET. Excitation and quenching mechanisms in the near-UV photodissociation of CH3Br and CH3Cl adsorbed on D2O or CH3OH on Cu(110). Phys Chem Chem Phys 2015; 17:9173-85. [PMID: 25757378 DOI: 10.1039/c4cp06128d] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Photochemical processes for CH3X (X = Cl, Br, I) adsorbed on top of thin films of D2O or CH3OH on a Cu(110) substrate is studied by time-of-flight mass spectrometry for a range of UV wavelengths (351-193 nm). Photodissociation via dissociative electron attachment by photoelectrons and by neutral photodissociation is identified and quantified based on the observed dynamics of the desorbing CH3 fragments. Photoelectron-driven dissociation of CH3X is found to be a maximum for monolayer quantities of the D2O or CH3OH on Cu(110), but with differing kinetic energy release on the two substrates. The dynamics of CH3Br and CH3Cl photodissociation qualitatively differ on CH3OH/Cu(110) as compared to D2O/Cu(110), which is ascribed to differing molecular structures for these systems. Evidence is presented for an efficient inter-molecular quenching mechanism for neutral photoexcitation of CH3Cl and CH3Br on the CH3OH/Cu(110) substrate.
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Affiliation(s)
- E T Jensen
- Department of Physics, University of Northern BC, 3333 University, Way, Prince George B.C., V2N 4Z9, Canada.
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Stähler J, Deinert JC, Wegkamp D, Hagen S, Wolf M. Real-time measurement of the vertical binding energy during the birth of a solvated electron. J Am Chem Soc 2015; 137:3520-4. [PMID: 25611976 DOI: 10.1021/ja511571y] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Using femtosecond time-resolved two-photon photoelectron spectroscopy, we determine (i) the vertical binding energy (VBE = 0.8 eV) of electrons in the conduction band in supported amorphous solid water (ASW) layers, (ii) the time scale of ultrafast trapping at pre-existing sites (22 fs), and (iii) the initial VBE (1.4 eV) of solvated electrons before significant molecular reorganization sets in. Our results suggest that the excess electron dynamics prior to solvation are representative for bulk ASW.
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Affiliation(s)
- Julia Stähler
- Abteilung Physikalische Chemie, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin, Germany
| | - Jan-Christoph Deinert
- Abteilung Physikalische Chemie, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin, Germany
| | - Daniel Wegkamp
- Abteilung Physikalische Chemie, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin, Germany
| | - Sebastian Hagen
- Abteilung Physikalische Chemie, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin, Germany
| | - Martin Wolf
- Abteilung Physikalische Chemie, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin, Germany
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