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Sakr NI, Kizilkaya O, Carlson SF, Chan S, Oumnov RA, Catano J, Kurtz RL, Hall RW, Poliakoff ED, Sprunger PT. Formation of Environmentally Persistent Free Radicals (EPFRs) on the Phenol-Dosed α-Fe 2O 3(0001) Surface. J Phys Chem C Nanomater Interfaces 2021; 125:21882-21890. [PMID: 34992708 PMCID: PMC8725784 DOI: 10.1021/acs.jpcc.1c04298] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Environmentally persistent free radicals (EPFRs) are a class of toxic air pollutants that are found to form by the chemisorption of substituted aromatic molecules on the surface of metal oxides. In this study, we employ X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS) to perform a temperature-dependent study of phenol adsorption on α-Fe2O3(0001) to probe the radical formation mechanism by monitoring changes in the electronic structure of both the adsorbed phenol and metal oxide substrate. Upon dosing at room temperature, new phenol-derived electronic states have been clearly observed in the UPS spectrum at saturation coverage. However, upon dosing at high temperature (>200 °C), both photoemission techniques have shown distinctive features that strongly suggest electron transfer from adsorbed phenol to Fe2O3 surface atoms and consequent formation of a surface radical. Consistent with the experiment, DFT calculations show that phenoxyl adsorption on the iron oxide surface at RT leads to a minor charge transfer to the adsorbed molecule. The experimental findings at high temperatures agree well with the EPFRs' proposed formation mechanism and can guide future experimental and computational studies.
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Affiliation(s)
- N I Sakr
- Department of Physics and Astronomy, Louisiana State University, Baton Rouge, Louisiana 70803, United States
| | - Orhan Kizilkaya
- Center for Advanced Microstructures and Devices, Louisiana State University, Baton Rouge, Louisiana 70806, United States
| | - Sierra F Carlson
- Department of Natural Sciences and Mathematics, Dominican University of California, San Rafael, California 94901, United States
| | - Simon Chan
- Department of Natural Sciences and Mathematics, Dominican University of California, San Rafael, California 94901, United States
| | - Reuben A Oumnov
- Department of Natural Sciences and Mathematics, Dominican University of California, San Rafael, California 94901, United States
| | - Jaqueline Catano
- Department of Natural Sciences and Mathematics, Dominican University of California, San Rafael, California 94901, United States
| | - Richard L Kurtz
- Department of Physics and Astronomy, Louisiana State University, Baton Rouge, Louisiana 70803, United States; Center for Advanced Microstructures and Devices, Louisiana State University, Baton Rouge, Louisiana 70806, United States
| | - Randall W Hall
- Department of Natural Sciences and Mathematics, Dominican University of California, San Rafael, California 94901, United States; Department of Chemistry, Louisiana State University, Baton Rouge, Louisiana 70803, United States
| | - E D Poliakoff
- Department of Chemistry, Louisiana State University, Baton Rouge, Louisiana 70803, United States
| | - Phillip T Sprunger
- Department of Physics and Astronomy, Louisiana State University, Baton Rouge, Louisiana 70803, United States; Center for Advanced Microstructures and Devices, Louisiana State University, Baton Rouge, Louisiana 70806, United States
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Patterson MC, DiTusa MF, McFerrin CA, Kurtz R, Hall RW, Poliakoff ED, Sprunger PT. Formation of environmentally persistent free radicals (EPFRs) on ZnO at room temperature: Implications for the fundamental model of EPFR generation. Chem Phys Lett 2017; 670:5-10. [PMID: 28824195 PMCID: PMC5560487 DOI: 10.1016/j.cplett.2016.12.061] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Environmentally persistent free radicals (EPFRs) have significant environmental and public health impacts. In this study, we demonstrate that EPFRs formed on ZnO nanoparticles provide two significant surprises. First, EPR spectroscopy shows that phenoxy radicals form readily on ZnO nanoparticles at room temperature, yielding EPR signals similar to those previously measured after 250°C exposures. Vibrational spectroscopy supports the conclusion that phenoxy-derived species chemisorb to ZnO nanoparticles under both exposure temperatures. Second, DFT calculations indicate that electrons are transferred from ZnO to the adsorbed organic (oxidizing the Zn), the opposite direction proposed by previous descriptions of EPFR formation on metal oxides.
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Affiliation(s)
| | - Mark F. DiTusa
- Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA 70803, USA
| | - Cheri A. McFerrin
- Department of Natural Sciences and Mathematics, Dominican University of California, San Rafael, CA 94901, USA
| | - R.L. Kurtz
- Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA 70803, USA
| | - Randall W. Hall
- Department of Natural Sciences and Mathematics, Dominican University of California, San Rafael, CA 94901, USA
| | - E. D. Poliakoff
- Department of Chemistry, Louisiana State University, Baton Rouge, LA 70803, USA
| | - P. T. Sprunger
- Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA 70803, USA
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3
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Wilson BP, Fulfer KD, Mondal S, Ren X, Tross J, Poliakoff ED, Jose J, Le AT, Lucchese RR, Trallero-Herrero C. High order harmonic generation from SF6: Deconvolution of macroscopic effects. J Chem Phys 2016; 145:224305. [DOI: 10.1063/1.4971244] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Affiliation(s)
- B. P. Wilson
- Department of Chemistry, Louisiana State University, Baton Rouge, Louisiana 70803, USA
| | - K. D. Fulfer
- Department of Chemistry, Louisiana State University, Baton Rouge, Louisiana 70803, USA
| | - S. Mondal
- J.R. Macdonald Laboratory, Kansas State University, Manhattan, Kansas 66506, USA
| | - X. Ren
- J.R. Macdonald Laboratory, Kansas State University, Manhattan, Kansas 66506, USA
| | - J. Tross
- J.R. Macdonald Laboratory, Kansas State University, Manhattan, Kansas 66506, USA
| | - E. D. Poliakoff
- Department of Chemistry, Louisiana State University, Baton Rouge, Louisiana 70803, USA
| | - J. Jose
- Department of Chemistry, Texas A&M University, College Station, Texas 77843, USA
- Department of Physics, Indian Institute of Technology Patna, Bihta 801103, India
| | - Anh-Thu Le
- J.R. Macdonald Laboratory, Kansas State University, Manhattan, Kansas 66506, USA
| | - R. R. Lucchese
- Department of Chemistry, Texas A&M University, College Station, Texas 77843, USA
| | - C. Trallero-Herrero
- J.R. Macdonald Laboratory, Kansas State University, Manhattan, Kansas 66506, USA
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4
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Affiliation(s)
- K. D. Fulfer
- Department of Chemistry, Louisiana State University, Baton Rouge, Louisiana 70803, USA
| | - D. Hardy
- Department of Chemistry, Louisiana State University, Baton Rouge, Louisiana 70803, USA
| | - A. A. Aguilar
- Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - E. D. Poliakoff
- Department of Chemistry, Louisiana State University, Baton Rouge, Louisiana 70803, USA
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5
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Patterson MC, Thibodeaux CA, Kizilkaya O, Kurtz RL, Poliakoff ED, Sprunger PT. Electronic signatures of a model pollutant-particle system: chemisorbed phenol on TiO₂(110). Langmuir 2015; 31:3869-3875. [PMID: 25774565 PMCID: PMC4407492 DOI: 10.1021/acs.langmuir.5b00030] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Environmentally persistent free radicals (EPFRs) are a class of composite organic/metal oxide pollutants that have recently been discovered to form from a wide variety of substituted benzenes chemisorbed to commonly encountered oxides. Although a qualitative understanding of EPFR formation on particulate metal oxides has been achieved, a detailed understanding of the charge transfer mechanism that must accompany the creation of an unpaired radical electron is lacking. In this study, we perform photoelectron spectroscopy and electron energy loss spectroscopy on a well-defined model system-phenol chemisorbed on TiO2(110) to directly observe changes in the electronic structure of the oxide and chemisorbed phenol as a function of adsorption temperature. We show strong evidence that, upon exposure at high temperature, empty states in the TiO2 are filled and the phenol HOMO is depopulated, as has been proposed in a conceptual model of EPFR formation. This experimental evidence of charge transfer provides a deeper understanding of the EPFR formation mechanism to guide future experimental and computational studies as well as potential environmental remediation strategies.
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Affiliation(s)
- Matthew C. Patterson
- Department of Physics and Astronomy, Louisiana State University, 202 Nicholson Hall, Baton Rouge, LA 70803
- Department of Chemistry, Louisiana State University, 232 Choppin Hall, Baton Rouge, LA 70803
| | - Chad A. Thibodeaux
- Department of Chemistry, Louisiana State University, 232 Choppin Hall, Baton Rouge, LA 70803
| | - Orhan Kizilkaya
- Center for Advanced Microstructures and Devices, Louisiana State University, 6980 Jefferson Highway, Baton Rouge, LA 70806
| | - Richard L. Kurtz
- Department of Physics and Astronomy, Louisiana State University, 202 Nicholson Hall, Baton Rouge, LA 70803
- Center for Advanced Microstructures and Devices, Louisiana State University, 6980 Jefferson Highway, Baton Rouge, LA 70806
| | - E. D. Poliakoff
- Department of Chemistry, Louisiana State University, 232 Choppin Hall, Baton Rouge, LA 70803
| | - Phillip T. Sprunger
- Department of Physics and Astronomy, Louisiana State University, 202 Nicholson Hall, Baton Rouge, LA 70803
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López-Domínguez JA, Lucchese RR, Fulfer KD, Hardy D, Poliakoff ED, Aguilar AA. Vibrationally specific photoionization cross sections of acrolein leading to the X̃A′2 ionic state. J Chem Phys 2014; 141:094301. [DOI: 10.1063/1.4893702] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Affiliation(s)
| | - Robert R. Lucchese
- Department of Chemistry, Texas A&M University, College Station, Texas 77843-3255, USA
| | - K. D. Fulfer
- Department of Chemistry, Louisiana State University, Baton Rouge, Louisiana 70803, USA
| | - David Hardy
- Department of Chemistry, Louisiana State University, Baton Rouge, Louisiana 70803, USA
| | - E. D. Poliakoff
- Department of Chemistry, Louisiana State University, Baton Rouge, Louisiana 70803, USA
| | - A. A. Aguilar
- Advanced Light Source, Lawrence Berkeley National Laboratory, University of California, Berkeley, California 94720, USA
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Kizilkaya O, Jiles RW, Patterson MC, Thibodeaux CA, Poliakoff ED, Sprunger PT, Kurtz RL, Morikawa E. High-throughput Toroidal Grating Beamline for Photoelectron Spectroscopy at CAMD. J Phys Conf Ser 2014; 493:012024. [PMID: 27134636 PMCID: PMC4851341 DOI: 10.1088/1742-6596/493/1/012024] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
A 5 meter toroidal grating (5m-TGM) beamline has been commissioned to deliver 28 mrad of bending magnet radiation to an ultrahigh vacuum endstation chamber to facilitate angle resolved photoelectron spectroscopy. The 5m-TGM beamline is equipped with Au-coated gratings with 300, 600 and 1200 lines/mm providing monochromatized synchrotron radiation in the energy ranges 25-70 eV, 50-120 eV and 100-240 eV, respectively. The beamline delivers excellent flux (~1014-1017 photons/sec/100mA) and a combined energy resolution of 189 meV for the beamline (at 1.0 mm slit opening) and HA-50 hemispherical analyzer was obtained at the Fermi level of polycrystalline gold crystal. Our preliminary photoelectron spectroscopy results of phenol adsorption on TiO2 (110) surface reveals the metal ion (Ti) oxidation.
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Affiliation(s)
- O Kizilkaya
- Center for Advanced Microstructures and Devices, Louisiana State University, Baton Rouge, LA 70806, USA
| | - R W Jiles
- Center for Advanced Microstructures and Devices, Louisiana State University, Baton Rouge, LA 70806, USA
| | - M C Patterson
- Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA 70803, USA
| | - C A Thibodeaux
- Department of Chemistry, Louisiana State University, Baton Rouge, LA 70803, USA
| | - E D Poliakoff
- Department of Chemistry, Louisiana State University, Baton Rouge, LA 70803, USA
| | - P T Sprunger
- Center for Advanced Microstructures and Devices, Louisiana State University, Baton Rouge, LA 70806, USA ; Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA 70803, USA
| | - R L Kurtz
- Center for Advanced Microstructures and Devices, Louisiana State University, Baton Rouge, LA 70806, USA ; Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA 70803, USA
| | - E Morikawa
- Center for Advanced Microstructures and Devices, Louisiana State University, Baton Rouge, LA 70806, USA
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Patterson MC, Keilbart ND, Kiruri LW, Thibodeaux CA, Lomnicki S, Kurtz RL, Poliakoff ED, Dellinger B, Sprunger PT. EPFR Formation from Phenol adsorption on Al2O 3 and TiO 2: EPR and EELS studies. Chem Phys 2013; 422:277-282. [PMID: 24443627 DOI: 10.1016/j.chemphys.2012.12.003] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
We have examined the formation of environmentally persistent free radicals (EPFRs) from phenol over alumina and titania using both powder and single-crystal samples. Electron paramagnetic resonance (EPR) studies of phenol adsorbed on metal oxide powders indicates radical formation on both titania and alumina, with both oxides forming one faster-decaying species (lifetime on the order of 50-100 hours) and one slower-decayng species (lifetimes on the order of 1000 hours or more). Electron energy loss spectroscopy (EELS) measurements comparing physisorbed phenol on single-crystal TiO2(110) to phenoxyl radicals on the same substrate indicate distinct changes in the π-π* transitions from phenol after radical formation. The identical shifts are observed from EELS studies of phenoxyl radicals on ultrathin alumina grown on NiAl(110), indicating that this shift in the π-π* transition may be taken as a general hallmark of phenoxyl radical formation.
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Affiliation(s)
- Matthew C Patterson
- Department of Physics and Astronomy, Louisiana State University, Baton Rouge, Louisiana 70803, USA
| | - Nathan D Keilbart
- Department of Physics and Astronomy, Louisiana State University, Baton Rouge, Louisiana 70803, USA ; Department of Mechanical Engineering, Brigham Young University-Idaho, Rexburg, ID 83460, USA
| | - Lucy W Kiruri
- Department of Chemistry, Louisiana State University, Baton Rouge, Louisiana 70803, USA
| | - Chad A Thibodeaux
- Department of Chemistry, Louisiana State University, Baton Rouge, Louisiana 70803, USA
| | - Slawo Lomnicki
- Department of Chemistry, Louisiana State University, Baton Rouge, Louisiana 70803, USA
| | - Richard L Kurtz
- Department of Physics and Astronomy, Louisiana State University, Baton Rouge, Louisiana 70803, USA
| | - E D Poliakoff
- Department of Chemistry, Louisiana State University, Baton Rouge, Louisiana 70803, USA
| | - Barry Dellinger
- Department of Chemistry, Louisiana State University, Baton Rouge, Louisiana 70803, USA
| | - Phillip T Sprunger
- Department of Physics and Astronomy, Louisiana State University, Baton Rouge, Louisiana 70803, USA
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Rathbone GJ, Poliakoff ED, Bozek JD, Toffoli D, Lucchese RR. Erratum: “Photoelectron trapping in N2O 7σ→kσ resonant ionization” [J. Chem. Phys. 123, 014307 (2005)]. J Chem Phys 2009. [DOI: 10.1063/1.3251046] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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10
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Affiliation(s)
- Robert R Lucchese
- Department of Chemistry, Texas A&M University, College Station, Texas 77843-3255, USA.
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Das A, Poliakoff ED, Lucchese RR, Bozek JD. Mode-specific photoionization dynamics of a simple asymmetric target: OCS. J Chem Phys 2009; 130:044302. [DOI: 10.1063/1.3062806] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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12
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Das A, Miller JS, Poliakoff ED, Lucchese RR, Bozek JD. Vibrationally resolved photoionization dynamics of CF4 in the DA12 state. J Chem Phys 2007; 127:044312. [PMID: 17672695 DOI: 10.1063/1.2749723] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Vibrationally resolved photoelectron spectroscopy of the CF4+ (D 2A1) state is studied for the first time over an extended energy range, 26.5<or=hnu<or=50 eV. It is found that the energy dependence of the totally symmetric stretching vibration is qualitatively different from all of the other vibrational modes. Moreover, the vibrational branching ratio curves for all of the symmetry forbidden vibrations are nearly identical. Qualitative arguments are used to show that it is likely that at least two shape resonances are present in the continuum, and that their characteristics, such as energy dependence and spatial localization, are distinctly different.
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Affiliation(s)
- Aloke Das
- Department of Chemistry, Louisiana State University, Baton Rouge, Louisiana 70803, USA
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Montuoro R, Lucchese RR, Bozek JD, Das A, Poliakoff ED. Quasibound continuum states in SiF4 (D̃A12) photoionization: Photoelectron-vibrational coupling. J Chem Phys 2007; 126:244309. [PMID: 17614551 DOI: 10.1063/1.2743430] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The authors report a fully vibrationally resolved photoelectron spectroscopy investigation of a nonplanar molecule studied over a range of excitation energies. Experimental results for all four fundamental vibrational modes are presented. In each case significant non-Franck-Condon effects are seen. The vibrational branching ratio for the totally symmetric mode nu1+ is found to be strongly affected by resonant excitation in the SiF4+ (D2A1) photoionization channel. This is shown to be the result of two distinct shape resonances, which for the first time have been both confirmed by theoretical calculations. Vibrationally resolved Schwinger photoionization calculations are used to understand the vibronic coupling for the photoelectrons, both using ab initio and harmonic vibrational wave functions.
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Affiliation(s)
- Raffaele Montuoro
- Department of Chemistry, Texas A&M University, College Station, Texas 77843-3255, USA
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Abstract
Evidence is presented demonstrating that an electron launched into the continuum is trapped in an unprecedented quasibound state, namely, one that extends through the backbone of the six-member carbon ring of C6F6. The mode specificity of the vibrational sensitivity to the electron trapping provides an experimental signature for this phenomenon, while adiabatic static model-exchange scattering calculations are used to map the wave function, which corroborate the interpretation.
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Affiliation(s)
- Aloke Das
- Department of Chemistry, Louisiana State University, Baton Rouge, Louisiana 70803, USA
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Rathbone GJ, Poliakoff ED, Bozek JD, Toffoli D, Lucchese RR. Photoelectron trapping in N2O 7sigma-->ksigma resonant ionization. J Chem Phys 2005; 123:014307. [PMID: 16035835 DOI: 10.1063/1.1946738] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Vibrationally resolved photoelectron spectroscopy of the N2O+(A 2Sigma+) state is used to compare the dependence of the photoelectron dynamics on molecular geometry for two shape resonances in the same ionization channel. Spectra are acquired over the photon energy range of 18< or =hv< or =55 eV. There are three single-channel resonances in this range, two in the 7sigma-->ksigma channel and one in the 7sigma-->kpi channel. Vibrational branching ratio curves are determined by measuring vibrationally resolved photoelectron spectra as a function of photon energy, and theoretical branching ratio curves are generated via Schwinger variational scattering calculations. In the region 30< or =hv< or =40 eV, there are two shape resonances (ksigma and kpi). The ksigma ionization resonance is clearly visible in vibrationally resolved measurements at hv=35 eV, even though the total cross section in this channel is dwarfed by the cross section in the degenerate, more slowly varying 7sigma-->kpi channel. This ksigma resonance is manifested in non-Franck-Condon behavior in the approximately antisymmetric v3 stretching mode, but it is not visible in the branching ratio curve for the approximately symmetric v1 stretch. The behavior of the 35-eV ksigma resonance is compared to a previously studied N2O 7sigma-->ksigma shape resonance at lower energy. The mode sensitivity of the 35-eV ksigma resonance is the opposite of what was observed for the lower-energy resonance. The contrasting mode-specific behavior observed for the high- and low-energy 7sigma-->ksigma resonances can be explained on the basis of the "approximate" symmetry of the quasibound photoelectron resonant wave function, and the contrasting behavior reflects differences in the continuum electron trapping. An examination of the geometry dependence of the photoelectron dipole matrix elements shows that the ksigma resonances have qualitatively different dependences on the individual bond lengths. The low-energy resonance is influenced only by changes in the end-to-end length of the molecule, whereas the higher-energy resonance depends on the individual N-N and N-O bond lengths. Branching ratios are determined for several vibrational levels, including the symmetry-forbidden bending mode, and all of the observed behavior is explained in the context of an independent particle, Born-Oppenheimer framework.
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Affiliation(s)
- G J Rathbone
- Department of Chemistry, Louisiana State University, Baton Rouge, Louisiana 70803, USA
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Rathbone GJ, Poliakoff ED, Bozek JD, Lucchese RR. Electronically forbidden (5σu→kσu) photoionization of CS2: Mode-specific electronic-vibrational coupling. J Chem Phys 2005; 122:064308. [PMID: 15740373 DOI: 10.1063/1.1850474] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Vibrationally resolved photoelectron spectroscopy of the CS(2) (+)(B (2)Sigma(u) (+)) state is used to show how nontotally symmetric vibrations "activate" a forbidden electronic transition in the photoionization continuum, specifically, a 5sigma(u)-->ksigma(u) shape resonance, that would be inaccessible in the absence of a symmetry breaking vibration. This electronic channel is forbidden owing to inversion symmetry selection rules, but it can be accessed when a nonsymmetric vibration is excited, such as bending or antisymmetric stretching. Photoelectron spectra are acquired for photon energies 17</=hnu</=72 eV, and it is observed that the forbidden vibrational transitions are selectively enhanced in the region of a symmetry-forbidden continuum shape resonance centered at hnu approximately 42 eV. Schwinger variational calculations are performed to analyze the data, and the theoretical analysis demonstrates that the observed forbidden transitions are due to photoelectron-mediated vibronic coupling, rather than interchannel Herzberg-Teller mixing. We observe and explain the counterintuitive result that some vibrational branching ratios vary strongly with energy in the region of the resonance, even though the resonance position and width are not appreciably influenced by geometry changes that correspond to the affected vibrations. In addition, we find that another resonant channel, 5sigma(u)-->kpi(g), influences the symmetric stretch branching ratio. All of the observed effects can be understood within the framework of the Chase adiabatic approximation, i.e., the Born-Oppenheimer approximation applied to photoionization.
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Affiliation(s)
- G J Rathbone
- Department of Chemistry, Louisiana State University, Baton Rouge, Louisiana 70803, USA
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Abstract
We discuss the excitation of forbidden vibrational transitions accompanying photoionization of linear triatomic molecules. Excitation of a single quantum of the antisymmetric stretching vibration is observed for mole cules with inversion symmetry, as is the bending mode. Photoelectron spectra of the N2O+(A2Π), CO2+(C2Σg+), and CS2+(B2Σu+) states obtained over a range of ionization energies exhibit contrasting behavior for the relative intensities of the forbidden vibrations. These energy-dependent vibrational branching ratios are shown to result from an intrachannel vibronic coupling mechanism. Moreover, this intrachannel coupling can be further divided into two cases, one in which the photoionization cross section is sensitive to geometry changes, and a second case in which it is not. These different cases can be distinguished by comparing the experimental and theoretical results for all three molecules.Key words: photoelectron spectroscopy, vibronic coupling, photoionization.PACS Nos.: 33.60.Cv, 33.20.Ni, 33.20.Wr, 33.80.Eh
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Rathbone GJ, Poliakoff ED, Bozek JD, Lucchese RR. Observation of the symmetry-forbidden 5sigmau-->ksigmau CS2 transition: a vibrationally driven photoionization resonance. Phys Rev Lett 2004; 92:143002. [PMID: 15089534 DOI: 10.1103/physrevlett.92.143002] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/18/2003] [Indexed: 05/24/2023]
Abstract
Vibrationally resolved photoelectron spectroscopy and Schwinger calculations are used to characterize a new resonance phenomenon in the 5sigma(u)-->ksigma(u) photoionization of CS2. This resonant channel is symmetry forbidden, yet is observable because it is activated by the antisymmetric stretching vibration. In addition, we show that a Franck-Condon breakdown occurs even though the energy dependence of the cross section is insensitive to geometry changes, which is unprecedented in photoionization.
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Affiliation(s)
- G J Rathbone
- Department of Chemistry, Louisiana State University, Baton Rouge, Louisiana 70803, USA
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19
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Abstract
We report results of experimental and theoretical studies of the vibrational branching ratios for CO 4sigma(-1) photoionization from 20 to 185 eV. Comparison with results for the 2sigma(u)(-1) channel of the isoelectronic N2 molecule shows the branching ratios for these two systems to be qualitatively different due to the underlying scattering dynamics: CO has a shape resonance at low energy but lacks a Cooper minimum at higher energies whereas the situation is reversed for N2.
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Affiliation(s)
- G J Rathbone
- Department of Chemistry, Louisiana State University, Baton Rouge, Louisiana 70803, USA
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20
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Abstract
Using high-resolution photoelectron spectroscopy, we have determined the energy dependent vibrational branching ratios for the symmetric stretch [v+ = (100)], bend [v+ = (010)], and antisymmetric stretch [v+ = (001)], as well as several overtones and combination bands in the 4sigmag(-1) photoionization of CO2. Data were acquired over the range from 20-110 eV, and this wide spectral coverage highlighted that alternative vibrational modes exhibit contrasting behavior, even over a range usually considered to be dominated by atomic effects. Alternative vibrational modes exhibit qualitatively distinct energy dependences, and this contrasting mode-specific behavior underscores the point that vibrationally resolved measurements reflect the sensitivity of the electron scattering dynamics to well-defined changes in molecular geometry. In particular, such energy-dependent studies help to elucidate the mechanism(s) responsible for populating the symmetry forbidden vibrational levels [i.e., v+ =( 010), (001), (030), and (110)]. This is the first study in which vibrationally resolved data have been acquired as a function of energy for all of the vibrational modes of a polyatomic system. Theoretical Schwinger variational calculations are used to interpret the experimental data, and they indicate that a 4sigmag-->ksigmau shape resonance is responsible for most of the excursions observed for the vibrational branching ratios. Generally, the energy dependent trends are reproduced well by theory, but a notable exception is the symmetric stretch vibrational branching ratio. The calculated results display a strong peak in the vibrational branching ratio while the experimental data show a pronounced minimum. This suggests an interference mechanism that is not accounted for in the single-channel adiabatic-nuclei calculations. Electronic branching ratios were also measured and compared to the vibrational branching ratios to assess the relative contributions of interchannel (i.e., Herzberg-Teller) versus intrachannel (i.e., photoelectron-mediated) coupling.
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Affiliation(s)
- G J Rathbone
- Department of Chemistry, Louisiana State University, Baton Rouge, Louisiana 70803, USA
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Affiliation(s)
- E. E. Doomes
- Department of Chemistry and Center for Advanced Microstructures and Devices, Louisiana State University, Baton Rouge, Louisiana 70803
| | - P. N. Floriano
- Department of Chemistry and Center for Advanced Microstructures and Devices, Louisiana State University, Baton Rouge, Louisiana 70803
| | - R. W. Tittsworth
- Department of Chemistry and Center for Advanced Microstructures and Devices, Louisiana State University, Baton Rouge, Louisiana 70803
| | - R. L. McCarley
- Department of Chemistry and Center for Advanced Microstructures and Devices, Louisiana State University, Baton Rouge, Louisiana 70803
| | - E. D. Poliakoff
- Department of Chemistry and Center for Advanced Microstructures and Devices, Louisiana State University, Baton Rouge, Louisiana 70803
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Farquar GR, Alderman SL, Poliakoff ED, Dellinger B. X-ray spectroscopic studies of the high temperature reduction of Cu(II)O by 2-chlorophenol on a simulated fly ash surface. Environ Sci Technol 2003; 37:931-5. [PMID: 12666923 DOI: 10.1021/es020838h] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
The reaction of 2-chlorophenol on Cu(II)O at 375 degrees C is studied using X-ray absorption near edge structure (XANES) spectroscopy. A mixture of copper(II) oxide and silica is prepared to serve as a surrogate for fly ash in combustion systems. 2-Chlorophenol is utilized as a model precursor for formation of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/F). The Cu K-edge spectra shiftto lower binding energy, reflecting the reduction of the copper. The substrate is found to form a mixture of Cu(II), Cu(I), and Cu(O), with the dominant species being Cu(I). The data are fitted well with a first-order reaction scheme, with a time constant at 375 degrees C of 76 s. This is the first application of XANES spectroscopy for studying the kinetics and mechanism of heterogeneous reactions relevant to combustion processes, and the results demonstrate the utility and desirability of such X-ray spectroscopic studies.
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Affiliation(s)
- George R Farquar
- Department of Chemistry, Louisiana State University, Baton Rouge, Louisiana 70803, USA
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Das R, Wu C, Mihill AG, Poliakoff ED, Wang K, McKoy V. Photoion Alignment: Chemical Signatures 200 eV above Threshold. ACTA ACUST UNITED AC 2002. [DOI: 10.1021/j100006a016] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Farquar GR, Miller JS, Poliakoff ED, Wang K, McKoy V. Rotationally resolved photoionization: Influence of the 4σ→kσ shape resonance on CO+(B 2Σ+) rotational distributions. J Chem Phys 2001. [DOI: 10.1063/1.1415463] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
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Floriano PN, Noble CO, Schoonmaker JM, Poliakoff ED, McCarley RL. Cu(0) nanoclusters derived from poly(propylene imine) dendrimer complexes of Cu(II). J Am Chem Soc 2001; 123:10545-53. [PMID: 11673986 DOI: 10.1021/ja010549d] [Citation(s) in RCA: 72] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
A family of diaminobutane core, poly(propylene imine) dendrimers coordinated to Cu(II), DAB-Am(n)-Cu(II)x (n = 4, 8, 16, 32, 64, x = n/2), was studied by means of extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES) spectroscopies. The geometry of the dipropylene triamine (dpt)-Cu(II) end-group complexes for all dendrimer generations is reported for the first time and is found to be that of a square-based pyramid with each Cu ion bound to three nitrogen atoms (Cu-N distance approximately 2.03 A) of the dpt end group of the dendrimer. An oxygen atom residing 1.96 A from the Cu ion also occupies the equatorial plane, and the pyramid is completed by an axial oxygen at approximately 2.65 A. In addition, we report for the first time that reduction of the Cu(II)-dendrimer complexes with NaBH4 yields DAB-Am(n)-Cu(0)(cluster) species. Transmission electron microscopy (TEM) studies of the reduced species demonstrate that there is a systematic decrease in the size of the generated Cu clusters with increasing dendrimer generation. Additionally, it was found that the size of the nanoclusters is a function of the n/x ratio of the DAB-Am(n)-Cu(II)x precursor, with highly monodisperse, extremely small nanoclusters (r(cluster) = 8.0 +/- 1.6 A) obtained with n = 64 and x = 16. EXAFS and XANES measurements on the reduced DAB-Am(n)-Cu(0)(cluster) corroborate the TEM data, and provide additional information on the possible encapsulation of the Cu nanoclusters by the dendrimers.
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Affiliation(s)
- P N Floriano
- Choppin Laboratories of Chemistry, Louisiana State University, Baton Rouge, Louisiana 70803-1804, USA
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Miller JS, Poliakoff ED, Miller TF, Natalense APP, Lucchese RR. Excitation of the symmetry forbidden bending mode in molecular photoionization. J Chem Phys 2001. [DOI: 10.1063/1.1349090] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Miller JS, Poliakoff ED. On the correlation between photoelectron energy and bending excitation in molecular photoionization. J Chem Phys 2000. [DOI: 10.1063/1.481869] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Rao RM, Poliakoff ED, Wang K, McKoy V. Molecular photoionization as a probe of vibrational–rotational–electronic correlations. J Chem Phys 1996. [DOI: 10.1063/1.471672] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Poliakoff ED, Choi HC, Rao RM, Mihill AG, Kakar S, Wang K, McKoy V. Photoion rotational distributions from near‐threshold to deep in the continuum. J Chem Phys 1995. [DOI: 10.1063/1.469751] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Choi HC, Rao RM, Mihill AG, Kakar S, Poliakoff ED, Wang K, McKoy V. Energy dependence of photoion rotational distributions of N2 and CO. Phys Rev Lett 1994; 72:44-47. [PMID: 10055562 DOI: 10.1103/physrevlett.72.44] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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Kelly LA, Duffy LM, Space B, Poliakoff ED, Roy P, Southworth SH, White MG. Vibrationally resolved shape resonant photoionization of N2O. J Chem Phys 1989. [DOI: 10.1063/1.456097] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Poliakoff ED, Kelly LA, Duffy LM, Space B, Roy P, Southworth SH, White MG. Vibrationally resolved electronic autoionization of core–hole resonances. J Chem Phys 1988. [DOI: 10.1063/1.454838] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Poliakoff ED, Ho M, Leroi GE, White MG. Constant ionic state spectroscopy of N2O. Dispersed fluorescence as a probe of molecular autoionization. J Chem Phys 1986. [DOI: 10.1063/1.451565] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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Poliakoff ED, Ho M, Leroi GE, White MG. Non‐Franck–Condon 2σ−1u vibrational distributions in N+2. An interchannel‐coupled shape resonance observed by dispersed fluorescence. J Chem Phys 1986. [DOI: 10.1063/1.449963] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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