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  • 1
    Electronic Resource
    Electronic Resource
    Near-threshold photoionization of nickel clusters: Ionization potentials for Ni3 to Ni90 (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 94-104 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The threshold photoionization efficiency (PIE) curves for nickel clusters in the size range Ni3 to Ni90 have been measured by laser photoionization with detection by time-of-flight mass spectrometry. Both warm (≤298 K) and cold (≤77 K) clusters have been studied. The PIE curves for 298 K clusters display thermal tails, while these tails are smaller for cold clusters. Cluster ionization potentials (I.P.s) have been determined by two methods: the Watanabe procedure and linear extrapolation of the PIE curves. Dramatic dependence of I.P. on cluster size is found for clusters smaller than 11 atoms, while the I.P.s of larger clusters decrease relatively smoothly and nearly monotonically from 5.84 eV for Ni11 to 5.56 eV for Ni90. The I.P.s for clusters larger than Ni40 show the linear dependence on reciprocal radius (R−1) predicted by the conducting spherical drop model of small particle I.P.s, but do not fit the model quantitatively unless the limiting (R−1→ 0) work function is reduced by 0.46 eV from the bulk polycrystalline value. The differences between the thermal tails of the room temperature and 77 K PIE curves diminish with increasing cluster size, suggesting a reduced difference between neutral and ionic structures for larger clusters. In general, there is poor agreement between our experimental results and theoretically calculated I.P.s for small nickel clusters, with the exception of the recently reported tight-binding theory results of Pastor et al. [Chem. Phys. Lett. 148, 459 (1988)].
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459467
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  • 2
    Electronic Resource
    Electronic Resource
    Photoionization studies of transition metal clusters: Ionization potentials for Fen and Con (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 1533-1539 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The photoionization efficiency (PIE) spectra for cold iron clusters (Fe6–Fe90) and cobalt clusters (Co3, Co7–Co92) have been measured using a tunable ultraviolet laser combined with time-of-flight mass spectrometry. Vertical ionization potentials (IPs) assigned from the observed photoionization thresholds decrease rapidly but nonmonotonically for both Fen and Con up to n≅20, beyond which IPs evolve more slowly and smoothly. The measured IPs for both iron and cobalt clusters are lower than those predicted by the conducting spherical droplet model. The evolution of IP with increasing cluster radius R is observed to occur more gradually than the R−1dependence predicted by this model. This suggests that the Fermi energy for clusters in this size range decreases with increasing cluster size. The shapes of the PIE spectra near threshold are observed to continuously evolve with increasing cluster size, with the smallest clusters displaying photoionization efficiencies which rapidly increase with energy above threshold, and larger clusters displaying spectra with more gradual slopes. It is proposed that this trend reflects the evolution in the density and distribution of low-lying electronic states which occurs with increasing cluster size.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459131
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  • 3
    Electronic Resource
    Electronic Resource
    Photoionization studies of niobium clusters: Ionization potentials for Nb2–Nb76 (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 5760-5767 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The photoionization efficiency (PIE) spectra for niobium clusters up to Nb76 are measured using laser ionization time-of-flight mass spectrometry. Ionization potentials (IPs) assigned from the PIE spectra evolve with the same general pattern observed for other transition metal clusters (Mn) studied to date: a rapid yet nonmonotonic decrease in IP to n(approximately-equal-to)15 followed thereafter by a relatively slow and smooth evolution. The measured IPs evolve with cluster radius R according to the predictions of the conducting spherical droplet model if the limiting (R→∞) IP is chosen to be 0.5 eV lower than the bulk polycrystalline work function. Kinetics experiments using D2 as the coreactant indicate the existence of two structural forms, one highly reactive, one relatively unreactive for clusters in the size range Nb9–Nb12, with the reactive forms predominant in each case. PIE spectra for Nb9–Nb12 were recorded using sufficient D2 added to the cluster source to selectively titrate the reactive forms of these clusters, leaving the unreactive forms as the predominant isomers. It is found that the unreactive forms of Nb9 and Nb12 possess higher IPs than those of the reactive forms, while both forms of Nb10 possess approximately the same IP.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459570
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  • 4
    Electronic Resource
    Electronic Resource
    Isomers of niobium clusters: Direct spectroscopic evidence (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 1476-1477 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have reproduced kinetics results indicating that niobium clusters in the size range Nb9–Nb12 are produced in two isomeric forms which possess widely different rates reactivity toward D2. We have exploited this difference in reactivity to record photoionization efficiency spectra of the unreactive forms of Nb9, Nb10, and Nb12 as well of a mixture containing predominantly the reactive forms. We find that the photoionization thresholds measured for Nb9 and Nb12 with the reactive forms of these species depleted via reaction with D2 are shifted to higher energies compared those recorded without D2 present. The photoionization threshold energies for both unreactive and reactive forms of Nb10 are approximately equal.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459159
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  • 5
    Electronic Resource
    Electronic Resource
    Photodissociation studies of microsolvated metal cation complexes Mg+(NCCH3)n (n=1–4) (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 4612-4619 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Acetonitrile-solvated Mg+ complexes Mg+(NCCH3)n were produced in a pick-up source. The Mg+(NCCH3)n clusters were subjected to photodissociation in a time-of-flight reflectron mass spectrometer. Except for a minor reactive product Mg+-NC at short wavelengths, only nonreactive (or evaporation) fragments were observed from photodissociation of Mg+(NCCH3)n (n=1–4). Action spectra of Mg+(NCCH3)n (n=1–4) were recorded in the spectral region of 230–560 nm, which provide insight into the structure and photodissociation dynamics of the complexes. For all the complexes we studied, the ligands are believed to be in the first solvation shell. Both the evaporation and reaction processes occur on the ground state surfaces of the complexes. By using the DFT/B3LYP and CIS methods, the most stable ground-state structures and the excitation spectra for Mg+(NCCH3)1–3 were obtained. The ab initio predictions appear to be consistent with the experimental results. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1394216
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  • 6
    Electronic Resource
    Electronic Resource
    Photodissociation spectroscopy of Mg+–C6H5X (X=H, F, Cl, Br) (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 10236-10246 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Photodissociation of a series of complexes Mg+–C6H5X (X=H, F, Cl, Br) has been studied. The formation of Mg+ was found to be the predominant dissociation pathway. We monitored the photodissociation product as a function of the excitation wavelength in a broad spectral region. Experiments on the complexes with different halide substitutions showed similar action spectra. This is explained by a similar structure shared by these complexes with Mg+ being above the benzene ring. In the photodissociation of Mg+–(C6H5F), MgF+ is also formed besides Mg+. The action spectra corresponding to these two channels were found to be different, and the MgF+ channel is believed to be from a different isomer. The experimental results are consistent with our quantum ab initio calculations. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.481706
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  • 7
    Electronic Resource
    Electronic Resource
    Photo-induced reactions in mass-selected complexes Mg+(FCH3)n, n=1–4 (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 3111-3120 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Photo-induced reactions in the metal cation–molecule complexes Mg+(CH3F)n have been studied as a function of the number of solvent molecules. While a photoreaction of the singly solvated complex Mg+-FCH3 yields exclusively CH3+, excitation of larger complexes Mg+(FCH3)2–4 produces predominantly bare and solvated MgF+. Photo-induced evaporation of the larger complexes was also observed, although with much lower yields. Possible mechanisms are suggested to interpret the abrupt change in the photoreaction patterns with an increasing complex size. The action spectra of all the complexes are discussed based on the transitions 2P←2S centered on the Mg+ ion but perturbed by the presence of the FCH3 molecules. Quantum ab initio calculations were performed to obtain the structures and action spectra of the complexes, which are directly compared with the experimental results. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1287143
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  • 8
    Electronic Resource
    Electronic Resource
    Photodissociation spectroscopy of the complexes of Mg+ with di- and tri-ethylamine (2002)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 116 (2002), S. 2896-2906 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present the photodissociation spectroscopy of the complexes of Mg+ with di- and tri-ethylamine in the spectral range of 230–440 nm. Mass spectrometry of the two parent complexes exhibits the persistent product Mg+ from nonreactive quenching throughout the whole wavelength range. As for the reactive channels, C3H7•-elimination products are dominant when the complexes are excited to 3Px,y. Furthermore, photoexcitation of Mg+–NH(C2H5)2 to 3Px,y yields a minor MgH-elimination fragment. On the other hand, photodissociation of Mg+–N(C2H5)3 produces charge-transfer fragments N+(C2H5)3 and (C2H5)2N+CH2. The action spectra of the two complexes consist of two pronounced peaks on the red and blue side of the Mg+ 3 2P←3 2S atomic transition. The calculated absorption spectra of the two complexes using the optimized structures of their ground states agree nicely with the observed action spectra. Photofragment branching fractions of the products are shown to be nearly independent of the photon energy for the 3Px,y excitation, indicating the importance of exit channel effects. A photoreaction mechanism is proposed for C3H7•-elimination, which entails Mg+ insertion into one C–N bond, followed by a nonadiabatic transition to the ground-state surface through a conical intersection. However, for the MgH-elimination channel in the photodissociation of Mg+–NH(C2H5)2, Mg+ rather inserts into the α-C–H bond. Finally, photoexcitation of Mg+–N(C2H5)3 leads to a prominent charge-transfer product [N+(C2H5)3]*, which dissociates further to (C2H5)2N+CH2 by a loss of CH3•. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1432995
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  • 9
    Electronic Resource
    Electronic Resource
    Studies of C60-metal reactions in the laser-ablation plasma of C60/M2O3 (M=La, Y, Eu, Gd) (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 189-192 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Reactions of excimer laser (XeCl, 308 nm) vaporized and excited fullerene C60 with La, Y, Eu, and Gd were carried out in mixtures of C60/La2O3, C60/Y2O3, C60/Eu2O3, and C60/Gd2O3. The reaction products M@xaC60, M@xaC60-2n and M@xaC60+2m (M=La, Y, Eu, and Gd) were identified by a reflectron type time-of-flight mass spectrometer (RTOFMS). The products were subjected to reactions with H2O, O2, and N2O in a pick-up source. The metallofullerenes were found to be nonreactive toward H2O, N2O, and O2. This gives support to the endohedral nature of the metallofullerenes. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469390
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  • 10
    Electronic Resource
    Electronic Resource
    Photofragmentation studies of small selenium cluster cations Sen+ (n=3–8) (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 7837-7843 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Selenium cluster cations are produced by the combination of laser vaporization and supersonic expansion techniques. Each small cluster cation Sen+ (n=3–8) is mass selected separately and subjected to one-photon laser photodissociation processes. The parent and daughter cluster ions are detected using a reflectron time-of-flight mass spectrometer. The appearance potentials of all the observed cluster fragment ions are estimated from their yield curves as a function of the laser wavelength. The neutral dimer evaporation is found to be the lowest energy photodissociation channel. In general, the odd-numbered cluster cations have much larger dissociation thresholds than those of the even-numbered cluster cations. In addition, the dissociation thresholds of the odd-numbered cations decrease with the increasing cluster size, while those of the even-numbered clusters increase with the increasing cluster size. A sequential neutral dimer evaporation mechanism is demonstrated in the photodissociation of some cluster cations at high photon energies. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.480119
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