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  • 1
    Digitale Medien
    Digitale Medien
    Photodetachment studies of extended excited states in I−Xen clusters (n=1–54) (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 6288-6297 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: We present a comprehensive experimental study of bound excited states in I−Xen clusters (n=1–54), using photoelectron spectroscopy and energy-dependent action spectroscopy. Starting at n=4, the electron detachment action spectra developed peaks lying in energy lower than the vertical binding energy. This behavior has been shown for both final spin states of the neutral iodine. It indicates the existence of bound electronic states extended over the xenon cluster. The peaks lying in energy below the J=1/2 detachment continuum of the iodine (n〉4) were detected over the whole cluster size range of I−Xen using electron detachment action spectroscopy. For the bound states relating to the J=3/2 continuum, in the size range n=4–12, thermionic emission has marked the existence of bound states. For n〉12, these states were stabilized and detected via two-photon excitations. The picture, unveiled from the above photoelectron and action spectra, is the gradual evolution of bound excited states on the xenon solvent cluster. The critical size for the binding of an excited electron is n=4. At the largest cluster interrogated, I−Xe54, the binding energy amounts to 170 meV. We compare these states to the ground electronic state of Xen− clusters, and discuss the differences between the experiments and model calculations. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.478533
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  • 2
    Digitale Medien
    Digitale Medien
    Resolution enhancement in the magnetic bottle photoelectron spectrometer by impulse electron deceleration (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 2543-2549 
    Details
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: We present a modified time of flight magnetic bottle photoelectron spectrometer (MBPES), designed to operate with mass-selected ion beams. It is based on a configuration in which the ion beam is coaxial with the electron flight tube. High resolution combined with high efficiency is achieved by applying impulse deceleration at the electron detachment zone immediately after detachment. The main effect of the impulse is to improve the resolution of the spectrometer by subtracting the ion velocity from the electron velocity. The impulse can also counteract the spread in the flight times caused by the alignment of the electrons in the magnetic bottle. Unlike previous designs of the MBPES, ultimate resolution is achieved without any loss in signal intensity. Resolutions of 8, 25, and 48 meV were obtained for 0.28, 1.22, and 2.11 eV electrons, respectively, with 60% collection efficiency. This design also allows easy switching between high-resolution high-yield and polarization-sensitive photoelectron spectroscopy modes. Our simulations indicate that, with careful attention to details, sub-meV resolution can be obtained using this approach. © 2001 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1367364
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  • 3
    Digitale Medien
    Digitale Medien
    A combined mass gate–energy discriminator (1997)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 4625-4626 
    Details
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: A mass gate allows transmitting a selected mass in a time-of-flight mass spectrometer and to block other masses. The conventional stopping-potential mass gate does not discriminate against spontaneous fragments, which are generated in the drift tube. We present a simple improved version of a mass gate, which discriminates against fragments by using the fact that their kinetic energy is lower than that of the parent ion. © 1997 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1148446
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  • 4
    Digitale Medien
    Digitale Medien
    Charge transfer excitations in the photoelectron spectrum of Cl−NH3: Experiment and calculation (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 6201-6204 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: A charge transfer (CT) excited state has been identified in the photoelectron spectrum of Cl−NH3. A narrow band at 4.0 eV binding energy (BE) is assigned to ionization of Cl−, and a broad band peaking at 6.45±0.15 eV BE corresponds to a CT state, Cl−NH+3. The assignments are confirmed by ab initio calculations, yielding binding energies of 3.88 and 6.36 eV.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.465913
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  • 5
    Digitale Medien
    Digitale Medien
    Photoelectron spectroscopy of iodine anion solvated in water clusters (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 9416-9419 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: We have measured the photoelectron spectra of clusters of I- solvated in water up to fifteen water molecules. The vertical binding energy of the electron increases with cluster size and levels off in clusters containing more than six water molecules. These results strongly indicate that the first solvation layer around the ion consists of six water molecules. This picture is quantitatively consistent with the photoelectron spectroscopy result of I- solvated in bulk water.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.461172
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  • 6
    Digitale Medien
    Digitale Medien
    The decay of triplet pyrazine and methylpyrazine in supersonic jets. Substitution effects (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 8095-8103 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: We have measured the decay rates of optically excited triplet states of pyrazine and methylpyrazine in a supersonic jet. The excess vibrational energy dependence of the radiationless rate constants in the energy range between the T1 and the S1 electronic origins of the isolated molecules was explored. Decay rates between 5×102 and 105 s−1 were found in the 1800 cm−1 range of excess vibrational energy above the origin of the T1 state in pyrazine. In methylpyrazine the decay rates increase from 8×102 to 3.3×104 in the first 600 cm−1 excess energy range above the T1 origin. The decay rates are free of mode specificity and rotational effects. The wide dynamic range of the T1→S0 radiationless rates of pyrazine is substantially enhanced by methyl substitution. The results support a model which suggests that certain vibrational modes, those which undergo large frequency decreases in the excited state, control the strong vibrational energy dependence of the T1→S0 intersystem crossing of pyrazine. These large frequency changes result from the interaction of the near lying 3nπ* and 3ππ* states (the "proximity effect''). The enhancement of the excess energy dependence of the decay rates by methyl substitution indicates a further decrease in the frequency of these modes. This effect of the methyl group is consistent with the "proximity effect.'' The frequency reduction of these modes in the S1 manifold of methylpyrazine also support this mechanism.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.462361
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  • 7
    Digitale Medien
    Digitale Medien
    The branching of nonradiative processes in isoquinoline (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 3532-3538 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: We have measured the absolute rates of internal conversion and of intersystem crossing in isoquinoline excited to its S2 vibronic states (3131–3062 A(ring)) in supersonic beams. The combination of direct detection of the triplets, absorption and excitation spectra allowed us to extract these rates. The intersystem crossing rate barely depends on the excess vibrational energy in the S2 manifold, being about 2×109 s−1. The internal conversion rates grow by more than two orders of magnitude over the range of 0–800 cm−1 of excess vibrational energy in the S2 state, up to 5×1010 s−1. At the S2 electronic origin intersystem crossing is the dominant nonradiative channel, while at vibrational energy exceeding 400 cm−1 internal conversion becomes dominant.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.456884
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  • 8
    Digitale Medien
    Digitale Medien
    The decay of triplet pyrazine in supersonic jets (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 7331-7339 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The decay rates of optically excited triplet states of pyrazine in supersonic expansion were measured by using three different methods. The excess energy dependence of the radiationless rate constants in the energy range between the T1 and the S1 electronic origins of the isolated molecule was explored. Decay rates between 7×102 –2.5×104 s−1 were found in the 1500 cm−1 range of excess vibrational energy from the origin of the T1 state. The decay rates are free of mode specificity and rotational effects. The pure radiative lifetime in the measured range is rovibronic independent. The results support a model which suggests that certain vibrational modes, those which undergo large frequency changes in the excited state, control the strong vibrational energy dependence of the T1 →S0 intersystem crossing of pyrazine.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.457306
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  • 9
    Digitale Medien
    Digitale Medien
    Proton transfer in neutral gas-phase clusters: α-Naphthol⋅(NH3)n (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 4127-4138 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Efficient excited-state proton transfer in neutral acid–base clusters α-naphthol⋅Bn has been detected and studied by a combination of laser spectroscopic techniques (resonant two-photon ionization, fluorescence excitation, and emission spectroscopy). S1 state proton transfer was observed for B=NH3 and n≥4, as evidenced by several criteria: (a) large red shift and substantial broadening of the R2PI spectra of the n≥4 clusters relative to those of the bare α-naphthol and smaller clusters; (b) very large Stokes shift (∼8000 cm−1) of the emission spectra of the n≥4 clusters; (c) complete broadening of the fluorescence emission band for the n≥4 clusters; and (d) a striking similarity of the emission band position and width of the latter spectra to the emission spectrum of the α-naphtholate anion in basic aqueous solution. No proton-transfer reaction was observed for small solvent clusters with B=NH3 and n≤3, nor for any of the pair complexes studied, which involve a single base partner [B=triethylamine, 3-dimethylamino-1-aminopropane, 1,4-bis(dimethylamino)butane] which we have studied so far. This behavior illustrates the difficulty of achieving charge separation in neutral gas-phase complexes or clusters. A critical gas-phase proton affinity PAcrit =248±3 kcal/mol was determined for proton transfer to take place in the α-naphthol⋅Bn (or base B) system.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.453820
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  • 10
    Digitale Medien
    Digitale Medien
    Dynamics of triplet states in beam-isolated benzaldehyde (1991)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 95 (1991), S. 7154-7164 
    Details
    Quelle: ACS Legacy Archives
    Thema: Chemie und Pharmazie , Physik
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1021/j100172a014
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