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  • 1
    ISSN: 1434-6079
    Keywords: 36.40 ; 34.40 ; 34.80.G
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract (CO2) n , (NO) n and (NH3) n clusters are generated in a supersonic molecular beam and size selected by scattering from an He beam. By measurements of angular dependent mass spectra, TOF distributions and the angular dependence of the scattered signal quantitative information on the fragmentation probability by electron impact is derived. The van der Waals systems (CO2) n and (NO) n appear only at masses which are simply multiples of the monomer mass. The preferred cluster ion is the monomer ion for all investigated cluster sizes withn=2 to 4. The fragment pattern for the quasi-hydrogen bonded (NH3) n -cluster shows, beside a large number of fragment masses, a preference for protonated ions. The results are explained in terms of simple models based on the structural change from the neutral to the ionized configuration and the fragmentation pattern of the monomer followed by ionmolecule reactions.
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  • 2
    ISSN: 1434-6079
    Keywords: 36.40 ; 82.50.F
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Infrared photodissociation spectra of (CH3NH2) n clusters were measured fromn=2 ton=6 near the monomer absorption of the C-N stretching mode at 1044 cm−1 using a cw-CO2 laser. The clusters were size-selected by scattering from a helium beam. The spectrum of cold dimers shows a red (1038 cm−1) and a blue (1048 cm−1) shifted peak which is attributed to the non-equivalent position of the C-N in the open dimer structure. The larger clusters exhibit only one peak between 1045.4 cm−1 and 1046.0 cm−1 caused by the equivalent position of the C-N in the cyclic structures of the larger clusters. Structure calculations confirm these results. Secondly, the mixed complexes C2H4-CH3COCH3 and C2H4-(CH3COCH3)2 were investigated. The dimer spectrum, measured around the monomer frequency of the out-of-plane bending mode of C2H4 at 949 cm−1, shows two peaks at 946.2 cm−1 and 961.3 cm−1. This splitting is attributed to two different isomers that are found in configuration calculations. A similar behaviour is found for the trimer.
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  • 3
    ISSN: 1434-6079
    Keywords: 36.40 ; 34.80.G
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The hydrogen-bonded (N2H4) n clusters and the van der Waals (OCS) n clusters are size selected in a scattering experiment with a He beam up to the cluster sizen=6. By measuring the angular distributions of the scattered clusters the complete fragmentation pattern of electron impact ionization is obtained. For Hydrazine the two main fragment masses are the protonated species (N2H4) n−1H+ and with somewhat weaker intensities also the nominal ion mass (N2H4) n + . The largest intensity is observed for the monomer ion N2H 4 + to which clusters up ton=5 fragment. For carbonylsulfide, completely different results are obtained. Aside from the fragments of the OCS monomer and the van der Waals cluster fragments (OCS) 2 + and (OCS) 3 + signals at mass S 2 + , S 3 + and S2OCS+ are detected. This indicates a fast chemical reaction in the cluster according to: S + OCS → CO + S2 which occurs for clusters of sizen ≥ 2. Peaks at S 3 + and S2OCS+ are seen for the first time forn ≥ 5 according to a further reaction of S2 in the cluster.
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  • 4
    ISSN: 1434-601X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The velocity dependence of the total cross section of Na-Hg has been measured in the velocity region from 750 to 2700 m/s. The extremaN=5.0 toN=11.0 are well resolved. The glory extrema indexing was performed by counting the number of measured rainbow extrema in the differential cross section at corresponding velocities. The results from the data evaluation method proposed by Bernstein and O'Brien are compared with the results from an inversion procedure for this system. Significant errors can result from the use of the Bernstein-O'Brien method except in the case of the expressiona 1ɛr m .
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  • 5
    ISSN: 1434-601X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Differential scattering cross sections for the collision partners Na-Kr and Na-Xe have been measured in the angular region of 3 to 30
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 185 (1965), S. 155-168 
    ISSN: 1434-601X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Total collision cross sections for the interaction between alkali atoms have been measured using a modulated atomic beam technique. Since the determination of the density in the scattering chamber is the main source of error in absolute scattering measurements, particular attention is given to this problem: The cross section for partnersA andB is measured first withA as beam particles anB as target particles, and then withB as beam particles andA as target particles. The data are used to deduce the long rangevan der Waals (inverse sixth power) potential constants, which can be compared with theoretically calculated values of different authors. The interaction constants resulting from the present measurements are in good agreement with those calculated byFontana, while other calculations give much larger values.
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  • 7
    ISSN: 1434-601X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The influence of the shape of the interatomic potential on the total and differential scattering cross section, with special consideration given to interference effects, was numerically studied with the help of a 5 parameter modified Lennard-Jones potential. It is shown that the experimental data for the systems Na-Kr and Na-Xe, for which precise measurements are available, can be well reproduced with the use of such a potential. The absolute value and velocity dependence of the total scattering cross section as well as rainbow scattering and rapid oscillations in the differential scattering cross section were all used in the comparison of the calculated with the experimental values. In addition, the modified potential has been used in a re-evaluation of recent experimental results for alkali metal —inert gas scattering.
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  • 8
    ISSN: 1434-6079
    Keywords: 36.40 ; 82.50.F
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The infrared photodissociation spectra of C2H4 and CH3OH dimers are measured for different internal excitation energies ΔE. The dimers are size-selected in a scattering process with He and the internal energy is varied by using (1) different collision energies, (2) different scattering angles and (3) by measuring the complete energy loss spectra with and without laser radiation by time-of-flight analysis of the scattered clusters. For (CH3OH)2 the width Γ of the spectrum increases strongly with ΔE, while the cross section at the maximum is constant, a normal behaviour for an inhomogeneously broadened system. For (C2H4)2 Γ is nearly constant after a sort of threshold and the cross section increases with increasing ΔE. These results are explained by hot band excitation and the coupling to the darkv 10-mode.
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  • 9
    ISSN: 1434-6079
    Keywords: PACS. 36.40.Mr Spectroscopy and geometrical structure of clusters
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: A method is presented for calculating vibrational spectra of clusters using intra- and intermolecular potential models of different origin. The two types of potentials are tuned and coupled to construct a total cluster potential. The determination of minima on this cluster potential energy surface, and the expansion of the potential about the minimum configurations makes it possible to apply standard spectroscopic methods. Starting from a normal mode analysis, harmonic and anharmonic frequency shifts are calculated using perturbational and variational methods for methanol clusters from the dimer to the hexamer. The results using the empirical OPLS potential model are compared with each other, with the harmonic line shift calculations for a calculated potential in the SCF approximation, and with the experimental data. There is an improvement with respect to the results obtained so far, however, the need for a better description of the intermolecular potential is pointed out.
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  • 10
    ISSN: 1434-6079
    Keywords: 36.40. +d ; 34.50.EZ
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Carbon dioxide clusters are generated in a supersonic molecular beam and size selected by scattering from a He beam. By analyzing the measured time-of-flight spectra as a function of the deflection angle, differential energy loss spectra for (CO2)2 — He are obtained which show a rotational rainbow structure with a maximal energy transfer of ΔE/E=0.4. This result is compatible with the slipped parallel structure of dimer but not with theT-shaped geometry. The scattering analysis is also used to derive information about the pressure dependence of cluster formation and the fragmentation by electron impact ionisation. The latter process leads preferably to the monomer product ion CO 2 + with a small but finite probability for other ionic channels.
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