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  • 1995-1999  (10)
  • 1990-1994  (11)
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  • 1
    Digitale Medien
    Digitale Medien
    Photoelectron spectra of dicarbon(1-) and ethynyl(1-) (1991)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 95 (1991), S. 1167-1177 
    Details
    Quelle: ACS Legacy Archives
    Thema: Chemie und Pharmazie , Physik
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1021/j100156a026
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  • 2
    Digitale Medien
    Digitale Medien
    The ultraviolet photoelectron spectrum of SO− (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 6926-6927 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The ultraviolet photoelectron spectrum (hν=3.531 eV) of SO− shows transitions to the three lowest lying electronic states of SO neutral. The electron affinity of SO was determined to be 1.125(5) eV. The harmonic vibrational frequency and the spin-orbit splitting of the SO− electronic ground state (2Π) were also determined. Franck–Condon analyses of the SO vibrational progressions were used in conjunction with the molecular constants of the well-characterized SO neutral molecule to determine the equilibrium bond length of SO− [re=1.570(5) A(ring)].
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.460223
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  • 3
    Digitale Medien
    Digitale Medien
    A study of the electronic structures of Pd−2 and Pd2 by photoelectron spectroscopy (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 4845-4853 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The ultraviolet negative ion photoelectron spectrum of Pd−2 is presented for electron binding energies up to 3.35 eV. The anion is prepared by sputtering in a flowing afterglow ion source. Multiple low-lying electronic states of Pd2, all unidentified previously, are observed with resolved vibrational structure. The spectrum shows two strong electronic bands, each with similar vibrational progressions. Franck–Condon analyses are carried out on the two transitions and molecular constants are extracted for the anion and the two neutral electronic states. With the help of simple molecular orbital arguments and ab initio calculations, these two electronic bands are assigned as the triplet ground state (3Σ+u) and a singlet excited state (1Σ+u). The adiabatic electron affinity is E.A.(Pd2)=1.685±0.008 eV and the singlet excitation energy T0(1Σ+u) is 0.497±0.008 eV (4008±65 cm−1 ). The bonding in the palladium dimers is discussed and we find that the anion bond strength is 1.123±0.013 eV stronger than that of the neutral. Related studies of Pd− yield an improved electron affinity of E.A.(Pd)=0.562±0.005 eV.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.461702
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  • 4
    Digitale Medien
    Digitale Medien
    Photoelectron spectroscopy of metal cluster anions: Cu−n, Ag−n, and Au−n (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 6987-7002 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Negative ion photoelectron spectra of Cu−n, Ag−n(n=1–10), and Au−n (n=1–5) are presented for electron binding energies up to 3.35 eV at an instrumental resolution of 6–9 meV. The metal cluster anions are prepared in a flowing afterglow ion source with a cold cathode dc discharge. In the spectra of Cu−2, Ag−2, and Au−2, the M2 X 1Σ+g←M−2 X 2Σ+u transitions are vibrationally resolved. We analyze these spectra to yield the adiabatic electron affinities, vibrational frequencies, bond length changes, and dissociation energies. The a 3Σ+u triplet states of Cu2 and Ag2 are also observed. Using experimental and theoretical data, we assign the major features in the Cu−3 and Ag−3 spectra to the transition from the linear ground state of the anion (M−31Σ+g) to an excited linear state of the neutral (M3 2Σ+u). The Au−3 spectrum is attributed to a two-photon process, photodissociation followed by photodetachment of the Au− or Au−2 fragment. For larger clusters, we measure the threshold and vertical detachment energies as a function of size. Trends in the electron affinities and excited state energy levels as a function of cluster size and composition are discussed in terms of simple models.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.459475
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  • 5
    Digitale Medien
    Digitale Medien
    Photoelectron spectroscopy of nickel group dimers: Ni−2, Pd−2, and Pt−2 (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 8542-8551 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Negative ion photoelectron spectra of Ni−2, Pd−2, and Pt−2 are presented for electron binding energies up to 3.35 eV at an instrumental resolution of 8–10 meV. The metal cluster anions are prepared in a flowing afterglow ion source. Each dimer exhibits multiple low-lying electronic states and a vibrationally resolved ground state transition. Franck–Condon analyses yield the anion and neutral vibrational frequencies and the bond length changes between anion and neutral. The electron affinities are determined to be EA(Ni2)=0.926±0.010 eV, EA(Pd2)=1.685±0.008 eV, and EA(Pt2)=1.898±0.008 eV. The electronic configurations of the ground states are tentatively assigned. Comparison of the nickel group dimers to the coinage metal dimers sheds light on the d orbital contribution to the metal bonding in the nickel group dimers.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.465577
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  • 6
    Digitale Medien
    Digitale Medien
    Chemisorption of carbon monoxide on platinum cluster anions (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 3575-3587 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Reactions of platinum cluster anions with carbon monoxide are investigated using a flow tube reactor (flowing afterglow) instrument. The platinum cluster anions are prepared with a cathodic discharge source. The cluster anions, Pt n−(n≤7), react with carbon monoxide in a flowing helium/argon buffer gas at 0.5 Torr total pressure and at 300 K. Clusters with four or more platinum metal atoms react by addition of CO with an effective bimolecular reaction rate of greater than 70% of the calculated collision rate, while for n=3 the reaction rate is 16% of the collision rate. At high CO concentrations, additional CO molecules attach to the clusters to form platinum carbonyl anion intermediates, with little loss of metal atoms. Saturation limits were found, above which no further CO addition occurred. The saturated cluster species are Pt3(CO)6−, Pt4(CO)8−, Pt5(CO)9−, and Pt6(CO)10−. The application of simple geometry arguments and electron counting rules to infer possible skeletal structures of the metal clusters is discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.466154
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  • 7
    Digitale Medien
    Digitale Medien
    Models for statistical decomposition of metal clusters: Vibrational frequency distributions (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 8458-8469 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The application of statistical theories to the decomposition kinetics of metal clusters requires the estimation of the vibrational frequency distributions. We adapt elastic theories developed for bulk metals and fine particles to generate a physically reasonable frequency distribution model for small metal clusters. Results obtained from this elastic cluster model compare favorably with previously reported experimental heat capacity data for fine particles. In addition, predictions of the present model are shown to correlate very well with experimentally determined trends in metal cluster cohesive energies. The elastic cluster model is then applied to the statistical unimolecular decay kinetics of metal clusters and compared with results found using earlier theoretical models. The present model predicts slower rates of decomposition in comparison with the other models. These results suggest that the binding energies extracted from experimental photodissociation and collision-induced dissociation measurements may have been slightly overestimated in the past. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.471595
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  • 8
    Digitale Medien
    Digitale Medien
    Models for statistical decomposition of metal clusters: Decay on multiple electronic states (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 8470-8484 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The inclusion of electronic degrees of freedom in the statistical unimolecular decomposition of metal clusters is considered using Rice–Ramsperger–Kassel–Marcus (RRKM) theory. All vibronic states are included in the sums and densities of states in both adiabatic and nonadiabatic treatments of the electronic states. To model the metal cluster electronic structure, a simple semiclassical treatment is used to calculate energy levels of electrons in a variable-size spherical cavity based on the Woods–Saxon radial potential. The potential parameters are adjusted to mimic the average level spacings and electron detachment energies of realistic metal clusters of various charge states. Direct permutations of the electron occupancies of these cluster electron energy levels generate a set of cluster electronic states, which are then used in numerical calculations of the vibronic sums and densities of states for the RRKM rates. The electronic corrections to the RRKM dissociation rates of the ground electronics states are presented for several examples to show trends with respect to cluster size, charge state, number of delocalized valence electrons, and dissociation energy. Inclusion of electronic degrees of freedom always reduces the cluster dissociation rate, by a few percent to a factor of 20 or more depending on cluster size, charge state, metal properties, and the excitation energy. The adiabatic and nonadiabatic approaches give quantitatively similar rates, except for the smallest cluster sizes. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.471596
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  • 9
    Digitale Medien
    Digitale Medien
    Nickel group cluster anion reactions with carbon monoxide: Rate coefficients and chemisorption efficiency (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 5715-5725 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Reactions of Ni−n(n=3–10), Pd−n(n=3–8), and Pt−n(n=3–7) with CO are studied in a flow tube reactor. Bimolecular rate coefficients are measured for the association reaction of CO adsorbing on the cluster surface. The rate coefficients range from about 10% of the collision rate for the trimer anions to near the collision rate for clusters larger than four atoms. The maximum number of CO molecules that bind to each cluster is determined. Whereas the saturation limits for nickel are typical for an 18 electron transition metal, the limits for platinum are lower, reflecting the electron deficient structures observed in condensed phase chemistry. The CO saturated palladium clusters represent the first examples of saturated binary palladium carbonyl compounds. Comparisons are made to similar studies on metal cation and neutral clusters and also to surface scattering studies of nickel group metals.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.467137
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  • 10
    Digitale Medien
    Digitale Medien
    Chemisorption and oxidation reactions of nickel group cluster anions with N2, O2, CO2, and N2O (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 7897-7906 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Reactions of nickel (Ni−n, n=3–10), palladium (Pd−n, n=3–8), and platinum (Pt−n, n=3–7) cluster anions are investigated in a flow tube reactor. Rate coefficients are measured for reactions with N2, O2, CO2, and N2O. Reactions with O2, CO2, and N2O have rates that are greater than 10% of the collision rate for most clusters of four atoms or larger, while N2 reactions generally exhibit much lower reaction efficiencies. All the reactions studied show a strong dependence on cluster elemental composition. Many of the palladium cluster reactions are significantly faster than the corresponding nickel and platinum cluster reactions, while Ni−n and Pt−n have similar rate coefficients. Pt−6 is observed to have anomalously low rate constants for reactions with N2, CO2, and N2O compared to neighboring platinum clusters sizes and the nickel and palladium hexamers. N2, CO2, and O2 reactions are generally association reactions with varying degrees of cluster fragmentation observed. N2O reactions result in sequential addition of O atoms to the cluster. The extent of cluster fragmentation for the various reagents can be correlated with the estimated exothermicities of the adsorption processes. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.470207
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