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  • 2000-2004  (6)
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  • 1
    Electronic Resource
    Electronic Resource
    Guided ion beam studies of the reactions of Vn+ (n=2–13) with D2: Cluster–deuteride bond energies as a chemical probe of cluster electronic structure (2002)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 116 (2002), S. 936-945 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The kinetic energy dependencies of the reactions of Vn+ (n=2–13) with D2 are studied in a guided ion beam tandem mass spectrometer. Products observed are VnD+ for all clusters and VnD2+ for n=4–13. All reactions are observed to exhibit thresholds, except for formation of VnD2+ for n=4,5,7,9,11–13. The enhanced reactivity of the odd-sized clusters towards D2 chemisorption is nicely correlated with the D0(Vn+–V) bond energies. The odd-number clusters are less stable and more reactive, suggesting that they are open shell, whereas the even-number clusters, which are more stable and less reactive, appear to be closed shell. Threshold analyses of the endothermic reactions lead to Vn+–D binding energies (n=1–13), which reach values comparable to the bulk phase for larger clusters. The Vn+–D bond energies show odd–even oscillations anticorrelated with D0(Vn+–V) for n〈5, but roughly parallel with D0(Vn+–V) for n〉5. Magnitude differences in the two series of bond energies suggest that the metal–metal bonding has appreciable 3d–3d contributions. The variation in the Vn+–D bond energies with cluster size is explained using promotion energy arguments. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1428342
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  • 2
    Electronic Resource
    Electronic Resource
    Modeling kinetic shifts in threshold collision-induced dissociation. Case study: Dichlorobenzene cation dissociation (2002)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 116 (2002), S. 5593-5602 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A threshold collision-induced dissociation (CID) study is performed on dichlorobenzene cation dissociation of both the ortho and para isomers. Ab initio calculations are performed on the system to investigate the details of the potential energy surface with respect to Cl atom loss and to provide the molecular parameters necessary for CID cross section modeling. The effects of kinetic shifts on the CID threshold determinations are investigated using a model that incorporates statistical unimolecular decay theory. The model is tested using unimolecular dissociation rate constants as a function of energy provided by earlier photoelectron–photoion-coincidence (PEPICO) experiments. The different possible sets of parameters involved in the CID model, their effect on the dissociation rates, and their effect on the final CID threshold determination are discussed. A tight transition state is observed to reproduce the experimental dissociation rates better than a phase-space limit loose transition state, a result attributed to a potential energy surface that is much more attractive than a simple ion-induced dipole potential. The dissociation thresholds derived from CID data are in reasonable agreement with the ones derived from fitting the PEPICO rates when similar transition state assumptions are used. A final analysis of the CID data yields 0 K dissociation energies for the Cl atom loss from dichlorobenzene of 3.22±0.17 eV for the ortho isomer and 3.32±0.18 eV for the para isomer. In the present study we support a mechanism that the dissociations of the two isomers proceed through a direct bond cleavage, rather than through isomerization to a common intermediate. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1458247
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  • 3
    Electronic Resource
    Electronic Resource
    Guided ion beam study of collision-induced dissociation dynamics: integral and differential cross sections (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 1213-1228 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The low energy collision-induced dissociation (CID) of Cr(CO)6+ with Xe is investigated using a recently modified guided ion beam tandem mass spectrometer, in the energy range from 0 to 5 eV in the center-of-mass (CM) frame. The additions to the instrument, updated with a double octopole system, and the new experimental methods available are described in detail. Integral cross sections for product formation are presented and analyzed using our standard modeling procedure. A slightly revised value for the bond dissociation energy of (CO)5Cr+–CO of 1.43±0.09 eV is obtained, in very good agreement with literature values. Axial and radial velocity distributions for primary and product ions are measured at 1.3, 2.0, and 2.7 eV, in the threshold region for product formation. The resulting velocity scattering maps are presented and discussed. Evidence of efficient energy transfer is observed from angular scattering of CID products. Experimental distributions of residual kinetic energies are derived and extend to zero, the point of 100% energy deposition. This indicates that energy transfer is nonimpulsive and probably associated with transient complex formation. For the first time, the experimental residual kinetic energy distributions are compared with the predictions of the empirical model used in integral cross section analyses. Good agreement is observed within experimental uncertainties. A model for the distribution of deposited energy during collisional activation is derived on the basis of these experimental observations. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1371958
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  • 4
    Electronic Resource
    Electronic Resource
    Activation of methane by size-selected iron cluster cations, Fen+ (n=2–15): Cluster-CHx (x=0–3) bond energies and reaction mechanisms (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 9747-9763 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The kinetic energy dependences of the reactions of Fen+ (n=2–15) with CD4 are studied in a guided ion beam tandem mass spectrometer over the energy range of 0–10 eV. All reactions exhibit thresholds and two main products, FenD+ and FenCD2+, are formed. These primary products decompose at higher energies to form secondary and higher order products, FenCD+, FenC+, Fen−1D+, Fen−1CD2+, Fen−1CD+, and Fen−1C+. The cross-section magnitudes for the dehydrogenation products, FenCD2+, are observed to vary considerably as a function of cluster size; subsequent dehydrogenation to form FenC+ becomes more facile for larger clusters. Thresholds for the various primary and secondary reactions are analyzed and bond energies for iron cluster cation bonds to C, CD, CD2, and CD3 are determined. As a function of cluster size, these bond energies rapidly reach relatively constant values, which are argued to lie close to bulk phase values. The relative magnitudes in these bond energies are consistent with simple bond order considerations. On the basis of this thermochemistry, we find that there are barriers to the primary dehydrogenation reactions for all the clusters, except n=3 and 4. Evidence that this barrier for n≥5 corresponds to the chemisorption step is discussed. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1413983
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  • 5
    Electronic Resource
    Electronic Resource
    Reactions of Pt+ with H2, D2, and HD: Effect of lanthanide contraction on reactivity and thermochemistry (2002)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 116 (2002), S. 5565-5573 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A guided ion beam tandem mass spectrometer is used to examine the kinetic energy dependence of reactions of the third-row transition metal cation, Pt+, with molecular hydrogen and its isotopologs. A flow tube ion source produces Pt+ ions in its electronic ground state term and primarily in the lowest spin–orbit level. Corresponding state-specific reaction cross sections are obtained. Modeling of the endothermic reaction cross sections yields the 0 K bond dissociation energy of D0(Pt+–H)=2.81±0.05 eV (271±5 kJ/mol). The experimental thermochemistry is consistent with ab initio calculations, performed here and in the literature. Theory also provides the electronic structures of these species and is used to examine the reactive potential energy surfaces. Results from reactions with HD provide insight into the reaction mechanisms and indicate that the late metal ion, Pt+, reacts largely via a direct mechanism. Results for this third-row transition metal system are compared with the first-row and second-row congeners and found to have higher reactivity towards dihydrogen and stronger M+–H bonds. These differences can be attributed to lanthanide contraction and relativistic effects. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1456028
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  • 6
    Electronic Resource
    Electronic Resource
    Reactions of Ta+ and W+ with H2, D2, and HD: Effect of lanthanide contraction and spin–orbit interactions on reactivity and thermochemistry (2002)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 116 (2002), S. 5574-5583 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A guided ion beam tandem mass spectrometer is used to examine the kinetic energy dependence of reactions of the third-row transition metal cations, Ta+, and W+, with molecular hydrogen and its isotopologs. A flow tube ion source produces Ta+ and W+ ions in their electronic ground state term and primarily in the lowest spin–orbit level. Corresponding state-specific reaction cross sections are obtained. Modeling of the endothermic reaction cross sections yields the 0 K bond dissociation energies in eV (kJ/mol) of D0(Ta+–H)=2.38±0.06 (230±6) and D0(W+–H)=2.27±0.05 (219±5). The experimental thermochemistry is consistent with ab initio calculations, performed here and from the literature, which also provide the electronic structures of these species and details about the reaction surfaces. Results from reactions with HD provide insight into the reaction mechanisms and indicate that these early metal ions, Ta+ and W+, react largely via insertion mechanisms. Results for these third-row transition metal systems are compared with the first-row and second-row congeners and found to have higher reactivity towards dihydrogen and stronger M+–H bonds. These differences can be attributed to the lanthanide contraction, relativistic effects, and efficient spin–orbit interactions among surfaces of different spin. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1456029
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