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  • American Institute of Physics (AIP)  (5)
  • 1990-1994  (5)
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  • 1
    Electronic Resource
    Electronic Resource
    Photodissociation dynamics of Mo(CO)6 at 266 and 355 nm: CO photofragment kinetic-energy and internal-state distributions (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 7937-7950 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The internal-state and kinetic-energy distributions of the CO photofragments from the 266 and 355 nm photolysis of Mo(CO)6 have been measured under collision-free conditions using vacuum-ultraviolet laser-induced fluorescence. The rotational-state distributions for CO(v‘=0) and (v‘=1) are well represented by Boltzmann distributions with effective rotational "temperatures'' of Tr(v‘=0)=950±70 K and Tr(v‘=1)=935±85 K for 266 nm and Tr(v‘=0)=750±70 K and Tr(v‘=1)=1150±250 K for 355 nm photolysis. The CO(v‘=1/v‘=0) vibrational-state ratios for 266 and 355 nm photolysis are 0.19±0.03 and 0.09±0.02, respectively. The Doppler-broadened CO photofragment line shapes indicate that the translational energy distributions are isotropic and Maxwellian. There is no photolysis-laser wavelength or internal-state dependence to the extracted translational "temperatures.'' The observed energy partitioning and kinetic-energy distributions are inconsistent with an impulsive ejection of a single CO ligand. CO photofragment line shapes for 266 nm photolysis are not consistent with a mechanism involving the repulsive ejection of the first CO ligand, followed by the statistical decomposition of the Mo(CO)5 fragment. While phase-space theories do not predict quantitatively the energy disposal, the photodissociation mechanism appears to be dominated by statistical considerations. The results also suggest that the photodissociation of Mo(CO)6 at 266 and 355 nm involves a common initial "state'' and that similar exit channel effects are operative.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460128
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  • 2
    Electronic Resource
    Electronic Resource
    Photodecomposition of Mo(CO)6/Si(111) 7×7: CO state-resolved evidence for excited state relaxation and quenching (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 2929-2939 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: State-resolved detection techniques have been used to characterize the ultraviolet photodecomposition dynamics of Mo(CO)6 on Si(111) 7×7 at 100 K. Details of the excitation/fragmentation mechanism including adsorbate energy transfer were examined by measuring the cross sections and the internal and translational energies of the photoejected CO from submonolayer through multilayer coverage regimes. The CO energy distributions are found to be independent of Mo(CO)6 coverage, and can be characterized by two components with markedly different mean energies. In contrast to the coverage independence of the measured energy disposal, the cross section was found to decrease by a factor of 3 from multilayer coverages to submonolayer coverages.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.467605
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  • 3
    Electronic Resource
    Electronic Resource
    Adsorption and photodecomposition of Mo(CO)6 on Si(111) 7×7: An infrared reflection absorption spectroscopy study (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 3187-3200 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The adsorption and photodecomposition of Mo(CO)6 adsorbed on Si(111) 7×7 surfaces has been studied with Auger electron spectroscopy, temperature programmed desorption, low energy electron diffraction and infrared reflection absorption spectroscopy in a single external reflection configuration. The external-reflection technique is demonstrated to have adequate sensitivity to characterize submonolayer coverages of photogenerated Mo(CO)x fragments. It is proposed that the first layer of Mo(CO)6 adsorbs in ordered islands with a Mo(CO)6 atop each adatom of the 7×7 reconstructed Si surface. UV irradiation of these islands produces a carbonyl fragment, identified as chemisorbed Mo(CO)5. The Mo(CO)5 thermally decarbonylates via two subcarbonyl intermediates with little CO dissociation. Photolysis of thicker layers results in the formation of Mox(CO)y dimers/polymers, as evidenced by the appearance of bridging CO, which is attributed to a facile association reaction. The dimer/polymer species correlate with deposition of C and O on the surface.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.466410
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  • 4
    Electronic Resource
    Electronic Resource
    State-resolved studies of the laser-induced desorption of NO from Si(111) 7×7: Low coverage results (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 2324-2338 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The results of a quantum-state-resolved study of the laser-induced desorption (LID) of NO from Si(111) 7×7 at a surface temperature of 100 K are reported. All aspects of the LID are found to be sensitive to the initial coverage. The coverage dependence indicates that there are two desorption mechanisms, one operative at low coverages that is quenched with increasing NO exposure, and one operative at high coverage. This report characterizes the low coverage channel. Most of the energy in the desorbed NO occurs as vibration and translation, with the rotations substantially cooler. The desorption is selective for production of the ground spin–orbit state. The energy partitioning shows strikingly little change as the desorption-laser wavelength was varied from 1907 to 355 nm. This, coupled with a quantitative study of the yield over the same photon energy range and selective coadsorption experiments, establishes that the desorption is specifically due to an interaction involving photogenerated holes in the rest-atom localized, intrinsic surface state of the 7×7 reconstructed surface. It is suggested that the surface state hole drives the desorption by neutralization of a NO−δ adsorbate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462029
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  • 5
    Electronic Resource
    Electronic Resource
    Photodecomposition dynamics of Mo(CO)6/Si(111) 7×7: CO internal state and translational energy distributions (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 7651-7654 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The rotational state and translational energy distributions of CO photodesorption products resulting from the 266 nm photolysis of Mo(CO)6 adsorbed on Si(111) 7×7 with coverages in the multilayer regime are reported. State-resolved measurements show two desorption components with highly disparate energy dispositions. Results for different surface temperatures indicate that the energy content in one component reaches quasi-equilibration with the surface temperature, which is attributed to collisional relaxation of nascent photodecomposition products within the adlayer. The other component exhibits disparate rotational and translational "temperatures'' that are significantly greater than, and independent of, the surface temperature. These nascent photodecomposition products are influenced by both energy quenching effects and dynamical constraints imposed by the existence of the adlayer.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.464705
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