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  • 1
    Electronic Resource
    Electronic Resource
    Reactions of iron clusters with oxygen and ethylene: Observation of particularly stable species (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 6579-6584 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Iron clusters have been produced by CO2-laser-induced decomposition of iron pentacarbonyl in a flow reactor. The absorption of CO2 laser photons was achieved by using SF6 as a sensitizer. By adding an oxidizing gas, N2O, or a hydrocarbon, C2H4, molecules which are also dissociated in the laser field, the iron clusters may react with several radicals. The as-synthesized species are extracted from the reaction zone by a conical nozzle and expanded into the source chamber of a cluster beam apparatus where they are analyzed with a time-of-flight mass spectrometer. In the experiment with N2O, we observe a magic peak at m=856 amu which can be readily assigned to the particularly stable Fe13O8 cluster. If C2H4 is added to the reactant gas, the mass spectrum reveals a magic peak at mass m=884 amu. Using deuterated ethylene, the magic peak shifts by 12 amu to larger masses, indicating that the magic cluster contains 12 hydrogen atoms. With the given restrictions, we readily derive the molecular formula Fe13C12H12. Chemical stability and symmetry considerations suggest that the detailed chemical formula of the magic cluster is Fe13(C2H2)6 and that its structure corresponds to a Fe13 icosahedron with six HC(Double Bond)CH or C(Double Bond)CH2 groups bound to six pairs of the 12 iron surface atoms. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1310596
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  • 2
    Electronic Resource
    Electronic Resource
    Deposition and analysis of silicon clusters generated by laser-induced gas phase reaction (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 5302-5306 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Silicon clusters have been generated by CO2-laser-induced decomposition of SiH4 in a flow reactor. By introducing a conical nozzle into the reaction zone, they are extracted into a molecular beam apparatus and analyzed with a time-of-flight mass spectrometer. The mass spectra show that the cluster source emits, besides small clusters, also nanosized species containing around 103 atoms. These clusters were deposited on silicon and sapphire targets at room temperature. The deposited films have been analyzed with a Raman spectrometer and with a field emission scanning electron microscope (FE-SEM). The Raman spectra reveal a broad amorphouslike band and a relatively sharp peak at 518.1 cm−1. Interpretation of the sharp Raman feature, based on the phonon confinement model, suggests the presence of silicon nanocrystallites in the deposited films with a particle size of about 3–3.6 nm in diameter. The FE-SEM micrographs show an agglomerate of spherical particles of 3–12 nm in diameter, with a pronounced maximum in the size distribution at around 3.5 nm. The various methods of characterization allow us to conclude that the size of the nanoclusters is largely preserved if they are deposited on the substrate. Therefore, the technique presented here might be an efficient means to produce silicon quantum dots of about 3 nm in diameter. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.360737
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  • 3
    Electronic Resource
    Electronic Resource
    The O–H stretching vibrations of glycine trapped in rare gas matrices and helium clusters (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 2978-2984 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Employing molecular beam depletion spectroscopy and Fourier transform infrared matrix spectroscopy, respectively, we have studied the O–H stretching vibrations of the glycine conformers I, II, and III. The glycine molecules were either deposited into large liquid helium clusters HeN, N¯=11000, THe=0.4 K) or trapped in various rare gas matrices (Ne, Ar, Kr) at temperatures below 12 K. By extrapolating the experimental data plotted as a function of the square root of the critical temperature of the matrix material, the positions of the gas phase absorption bands were estimated to be 3585±2 cm−1 (conformer I), 3295±3 cm−1 (conformer II), and 3580±5 cm−1 (conformer III). The experimental results are compared with recent ab initio calculations. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479580
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  • 4
    Electronic Resource
    Electronic Resource
    Laser-driven flow reactor as a cluster beam source (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 3833-3837 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A novel technique for the production of expansion-cooled cluster beams from materials with low vapor pressure is presented. The clusters are produced in a flow reactor from gas phase reactants by aggregation of CO2-laser-induced decomposition products. By introducing a conical nozzle into the reaction zone, they are extracted into a molecular beam apparatus and analyzed with a time-of-flight mass spectrometer. Depending on the type of CO2-laser employed, the source can be operated in the pulsed or continuous mode. The generation of carbon and silicon clusters is demonstrated by decomposing gaseous C2H2 and SiH4, respectively. The laser-driven cluster course is also employed to generate fullerenes and nanosized silicon particles. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1145445
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  • 5
    Electronic Resource
    Electronic Resource
    Infrared photodissociation of size selected internally excited ethylene clusters (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 6276-6283 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Ethylene clusters (C2H4)n are generated in a supersonic expansion with He and size selected by scattering from a helium beam. The clusters are dissociated upon absorption of a photon from a pulsed CO2 laser by exciting the ν7 mode of the monomer. During the collision about 30 meV of internal energy is transferred to the cluster so that the laser photons interact with internally hot clusters. The frequency and fluence dependences of the photodissociation cross sections are measured for (C2H4)n with n=2,3,4,5, and 6. Nearly all spectra exhibit structure which is most pronounced for the dimer. The overall width (FWHM) decreases from 31.2 cm−1 for the dimer to 12.2 cm−1 for the hexamer, while the maximum position is nearly the same (951.6 cm−1). The structure of the dimer spectrum is attributed to hot bands. The large linewidth corresponds to a short lifetime in the ps range.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453456
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  • 6
    Electronic Resource
    Electronic Resource
    Vibrational predissociation of ethylene dimers selectively prepared by molecular beam scattering (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 84 (1986), S. 1042-1044 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.450589
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  • 7
    Electronic Resource
    Electronic Resource
    CO2-laser induced photodissociation studies of size-selected small benzene clusters (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 5826-5834 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The infrared photodissociation of size-selected, small benzene clusters has been investigated in the region of the ν18 CH in-plane bend using a pulsed CO2 laser. By scattering the cluster beam with a secondary Ne beam and observing off-axis the effect of the laser irradiation with a rotatable mass spectrometer, cluster-specific spectroscopy is performed. The dependence of IR absorption and subsequent dissociation of (C6H6)n clusters has been investigated as a function of laser frequency and laser fluence for n=2, 3, and 4. The absorption profiles are structureless and show only little variation with cluster size. If, instead of He, Ne is used as carrier gas, the absorption profiles are distinctively narrower. This effect is attributed to a lower internal temperature achieved with Ne. In contrast to the benzene dimer and tetramer, the fluence dependence for the trimer dissociation is stronger than linear suggesting that more than one photon is needed to dissociate this cluster. In a computational approach, the structures of the benzene dimer, trimer, and tetramer have been calculated employing an energy minimization program. For the trimer a cyclic ring structure is determined. The computational results are in perfect agreement with the experimental findings.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458403
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  • 8
    Electronic Resource
    Electronic Resource
    New infrared injection-seeded optical parametric oscillator with high energy and narrow bandwidth output (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 62 (1993), S. 805-807 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report on a new infrared injection-seeded optical parametric oscillator with narrow bandwidth (Γ≤0.2 cm−1) and high energy (E≥4 mJ/pulse) output between 2.5 and 4 μm which has been developed for cluster spectroscopy in molecular beams. The oscillator contains a LiNbO3 crystal pumped by the 1.064 μm fundamental of a Q-switched Nd:YAG laser. In order to reduce the linewidth and to increase the output energy, it is seeded with narrow bandwidth IR-radiation obtained by difference frequency mixing the output of a tunable dye laser with the second harmonic of the same Nd:YAG laser in a LiIO3 crystal.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.108584
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  • 9
    Electronic Resource
    Electronic Resource
    The structures of small methyl fluoride clusters from infrared dissociation experiments (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 3021-3028 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Molecular beam depletion spectroscopy has been employed to study the dissociation of small methyl fluoride clusters upon excitation of the ν3 C–F stretch vibration at 1048.6 cm−1. Size selection has been achieved by dispersing the (CH3F)n cluster beam by a secondary rare gas beam. For the methyl fluoride dimer only very weak dissociation signals could be observed. The corresponding spectrum features a single, 13.4 cm−1 broad absorption line. This observation is explained with a symmetric dimer structure, in which both monomer units reside at equivalent positions, and an inefficient coupling of the molecular vibration to the intermolecular bond. For the trimer and tetramer very strong dissociation yields are observed. Whereas the trimer shows a complicated spectrum which is attributed to its nonsymmetric structure, the tetramer spectrum is again characterized by a single peak. In order to obtain supplementary information, dissociation spectra have also been measured for small methyl fluoride clusters residing inside or on the surface of large Arx host clusters. These matrixlike spectra are consistent with the free gas-phase cluster data. Finally, in a computational approach, the structures of the methyl fluoride dimer, trimer, and tetramer have been determined by total energy minimization. The theoretical results are in perfect agreement with the experimental findings.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463043
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  • 10
    Electronic Resource
    Electronic Resource
    Infrared photodissociation of size-selected small ammonia clusters
    Amsterdam : Elsevier
    Chemical Physics 126 (1988), S. 215-228 
    Details
    ISSN: 0301-0104
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0301-0104(88)85034-1
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