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  • 1
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Photoexcitation of size-selected hydrated electron clusters, (H2O)−n , in the near IR results in a competition between photofragmentation and electron photodetachment. To investigate the origin of this competition, the decay probability into ionic fragments for the n=25 cluster was measured as a function of photon energy from 0.91≤hν≤3.49 eV. The photofragmentation probability increases rapidly with decreasing excitation energy in the general vicinity of the vertical detachment energy of this cluster (1.4 eV) determined via photoelectron spectroscopy. This result suggests that fragmentation accompanies photoexcitation of the excess electron with near zero kinetic energy. Thus, photofragmentation appears to proceed through an optically prepared intermediate similar to that reached in electron scattering from neutral clusters, which displays an enhanced dissociative attachment pathway with near zero kinetic energy electrons.
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  • 2
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The negative ion photoelectron spectra of the oxide anion complexes O−Rg, Rg=Ar, Kr, and Xe, and O−N2 have been recorded. In each spectrum, two partially resolved peaks were observed, their relative intensities varying with source conditions. These peaks were assigned to photodetachment transitions from the 2Σ ground state and unresolved 2Π3/2,1/2 low-lying excited states of the anion. From our data we find dissociation energies and bond lengths for the 2Σ and 2Π anion states. Periodic trends in the bond length and dissociation energy are examined and compared to those in the isoelectronic neutral halogen rare gas systems and the effect of anisotropy in the interatomic potential and relative interaction strength is examined. From our data we find that the dissociation energies in the anion system are much larger but that the 2Σ-2Π splitting is significantly lower. In addition to the diatomic clusters, we report the photoelectron spectra of the O−Krn=2–5 and O−Xen=2–3 clusters and tabulate the vertical detachment energies and peak widths. From a comparison of the energetics and peak broadening we are able to make a determination of the general structure of the n=2 and n=3 clusters. © 2002 American Institute of Physics.
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  • 3
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The negative ion photoelectron spectra of the gas-phase, ion-neutral complexes; NO−(Ar)n=1–14, NO−(Kr)1, NO−(Xe)n=1–4, NO−(N2O)n=3–5, NO−(H2S)1, NO−(NH3)1, and NO−(EG)1 [EG=ethylene glycol] are reported herein, building on our previous photoelectron studies of NO−(N2O)1,2 and NO−(H2O)1,2. Anion solvation energetic and structural implications are explored as a function of cluster size in several of these and as a result of varying the nature of the solvent in others. Analysis of these spectra yields adiabatic electron affinities, total stabilization (solvation) energies, and stepwise stabilization (solvation) energies for each of the species studied. An examination of NO−(Ar)n=1–14 energetics as a function of cluster size reveals that its first solvation shell closes at n=12, with an icosahedral structure there strongly implied. This result is analogous to that previously found in our study of O−(Ar)n. Inspection of stepwise stabilization energy size dependencies, however, suggests drastically different structures for NO−(Ar)2 and O−(Ar)2, the former being "Y" shaped, and the latter being linear. While stepwise stabilization energies usually provide good estimates of ion–single solvent dissociation energies, in the cases of NO−(Ar)1, NO−(Kr)1, and NO−(Xe)1, it is possible to determine more precise values. A plot of these anion–solvent dissociation energies shows them to vary linearly with rare gas atom polarizability, confirming the dominance of an ion-induced dipole interaction in these complexes. Extrapolation of this trend permits the estimation of NO−(centered ellipsis) (rare gas atom) interaction energies for helium, neon, and radon, as well. The relative strengths of the molecular solvents, N2O, H2S, NH3, H2O, and EG are reflected in their stepwise stabilization energies and in the degree of broadening observed in their photoelectron spectra. © 2002 American Institute of Physics.
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  • 4
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present the mass spectral and photoelectron spectroscopic results of our study of (HF)2−. Our main findings are as follows. The (HF)2− anion was observed experimentally for the first time, confirming the 20 year old prediction of Jordan and Wendoloski. The photoelectron spectrum of (HF)2− exhibits a distinctive spectral signature, which we have come to recognize as being characteristic of dipole bound anions. The vertical detachment energy (VDE) of (HF)2− has been determined to be 63±3 meV, and the adiabatic electron affinity (EAa) of (HF)2 was judged to be close to this value as well. Relatively weak spectral features, characteristic of intramolecular vibrations in the final (neutral dimer) state, were also observed. We have interpreted these results in terms of slight distortions of the dimer anion's geometric structure which lead to an enhanced dipole moment. This interpretation is supported to a considerable extent by theoretical calculations reported in the companion paper by Gutowski and Skurski. © 1997 American Institute of Physics.
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  • 5
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 57-66 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present the photoelectron spectra of negatively charged cesium iodide nanocrystals recorded using 2.540 eV photons. The species examined were produced using an inert gas condensation cluster ion source, and they ranged in size from (CsI)−n=13 to nanocrystal anions comprised of 330 atoms. Nanocrystals showing two distinct types of photoemission behavior were observed. For (CsI)−n=13 and (CsI)−n=36−165, a plot of cluster anion photodetachment threshold energies vs n−1/3 gives a straight line extrapolating (at n−1/3=0, i.e., n=∞) to 2.2 eV, the photoelectric threshold energy for F centers in bulk cesium iodide. The linear extrapolation of the cluster anion data to the corresponding bulk property implies that the electron localization in these gas-phase nanocrystals is qualitatively similar to that of F centers in extended alkali halide crystals. These negatively charged cesium iodide nanocrystals are thus shown to support embryonic forms of F centers, which mature with increasing cluster size toward condensed phase impurity centers. Under an alternative set of source conditions, nanocrystals were produced which showed significantly lower photodetachment thresholds than the aforementioned F-center cluster anions. For these species, containing 83–131 atoms, a plot of their cluster anion photodetachment threshold energies versus n−1/3 gives a straight line which extrapolates to 1.4 eV. This value is in accord with the expected photoelectric threshold energy for F' centers in bulk cesium iodide, i.e., color centers with two excess electrons in a single defect site. These nanocrystals are interpreted to be the embryonic F'-center containing species, Cs(CsI)−n=41−65. © 1995 American Institute of Physics.
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  • 6
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 1884-1888 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present negative ion photoelectron spectra of the smallest stable molecular negative ion, the lithium hydride anion. Photoelectron spectra, recorded using 2.540 eV photons, are reported for the LiH(D) [X 1Σ+]+e−←LiH(D)−[X 2Σ+] transitions of 7LiH− and 7LiD−. Adiabatic electron affinities of 0.342±0.012 eV and 0.337±0.012 eV were determined for 7LiH and 7LiD, respectively. The experimentally determined electron affinities led to anion dissociation energy (D0) values of 2.017±0.021 eV for 7LiH− and 2.034±0.021 eV for 7LiD− relative to their Li[2S1/2]+H−(D−)[1S0] asymptotes. Franck–Condon analyses yielded the following molecular parameters for the ground state of 7LiH−: Be=6.43±0.18 cm−1, re=1.724±0.025 A(ring), and ωe=920±80 cm−1; and the following parameters for the ground state of 7LiD−: Be=3.62±0.06 cm−1, re=1.724±0.015 A(ring), and ωe=650±45 cm−1. In addition, we have observed the alkali hydride anions: 7LiH−2, 7LiD−2, Li2D−, NaD−, NaD−2, NaD−3, and NaD−4. No photodetachment signal was observed for the lithium dihydride anion, 7LiD−2, using 2.540 eV photons.
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  • 7
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
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  • 8
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 39-47 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Negative ion photoelectron spectra of the solvated anion clusters O−(Ar)n=1–26,34 have been recorded. Vertical detachment energies obtained from the cluster anion spectra were used to determine total as well as stepwise stabilization energies. An examination of these energetic values as a function of cluster size demonstrates that the first solvation shell closes at n=12. Furthermore, magic numbers in the energetic data and in the mass spectrum suggest O−(Ar)n clusters of sizes n=12–34 are structurally very similar to homogeneous rare gas clusters and follow a polyicosahedral packing pattern, implying O−(Ar)12 has an icosahedral structure and O−(Ar)18 has a double icosahedral structure. The solvated cluster anion photoelectron data were also analyzed using a generalized cluster size equation, which relates the cluster anion data to bulk parameters. The data for O−(Ar)n≥12 is well represented by the theoretical prediction and was therefore used to estimate several bulk parameters, including the photoemission threshold, the photoconductivity threshold, and the bulk solvation energy. © 1995 American Institute of Physics.
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  • 9
    ISSN: 1572-8862
    Keywords: Zirconium oxides ; zirconia ; cluster anions ; mass spectrometry ; anion photoelectron spectroscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract We present a preliminary report on our mass spectrometric and photoelectron spectroscopic studies of zirconium oxide molecular and cluster anions using a newly built laser vaporization/time-of-flight/magnetic bottle, negative ion photoelectron spectrometer. This work was motivated in part by evidence which suggests that zirconium dioxide catalyzes the radiolysis of interfacial water. We present our mass spectrometric observations of oxygen-rich zirconium oxide cluster anions and our photoelectron spectra of ZrO− and ZrO 2 − . From the photoelectron spectrum of ZrO−, the adiabatic electron affinity of ZrO was determined to be 1.3±0.3 eV, and from this value, the dissociation energy of ZrO− (into Zr and O−) was found to be 7.8±0.3 eV. From the photoelectron spectrum of ZrO2, the adiabatic electron affinity of ZrO2 was determined to be 1.8±0.4 eV.
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  • 10
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 5514-5519 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Copper-doped aluminum cluster anions, CuAln− were generated in a laser vaporization source and examined via mass spectrometry (n=2–30) and anion photoelectron spectroscopy (n=2–15). The mass spectrum of the CuAln− series is dominated by CuAl13− with other magic numbers also appearing at n=6, 19, and 23. The electron affinity versus cluster size trend shows a peak at n=6 and a dip at n=13. These results are discussed in terms of the reordering of shell model energy levels and the enhanced stability of neutral CuAl13. Reordering, which is a consequence of the copper atom residing in the central region of these clusters, provides an anion-oriented electronic rationale for the observed magic numbers. © 2001 American Institute of Physics.
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