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  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 6215-6225 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A quasiclassical trajectory study of the Cs(7p)+H2→CsH+H harpooning reaction at thermal energies is carried out on a single potential energy surface. Extensive calculations are performed in a 2D space since 3D calculations show that all trajectories are nearly confined into the collision plane. Calculated rotational and angular distributions of CsH products are in good agreement with experimental data. The best agreement is obtained using a potential energy surface with no potential barrier in the exit valley. Some dynamical features are demonstrated through an analysis of correlations between various collision parameters. Migrations of the electronic charge "−'' from one H atom to the other during the collision induce important dynamical effects; in particular, they increase the collision time and reduce CsH product vibrational energy. The duration of the collision, the deflection angle, the angle between J' and L' (internal and orbital output angular momenta) and the translational energy of products are closely related to the impact parameter; there is a radical change in the behavior of the system according to the impact parameter being smaller or greater than the critical value bc(approximately-equal-to)2.8 A(ring). For b≤bc, the collision time is constant, the deflection function is linear, J' and L' are either parallel or antiparallel; for b≥bc, the collision time increases with b, an isotropic component appears in the deflection function, and J' and L' are always parallel. The geometry of approach has no influence on the dynamics of the collision. Angular and rotational distributions are not modified when taking into account the nonreactive channels correlated to Cs(6s,6p,5d,7s)+H2.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 434-444 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The Cs(7P)+H2→CsH (X 1Σ+) (v‘=0,J‘)+H reaction has been studied in a crossed-beam experiment, with electronic excitation of Cs atoms and laser-induced fluorescence detection of CsH products. The Doppler technique has been applied to determine the center of mass angular scattering probability of CsH products, for all rotational levels between 1 and 14 (in v‘=0) and for various values of the collision energy between 0.03 and 0.13 eV. We have used two complementary arrangements of the analysis laser beam: With a "parallel'' arrangement (the laser beam is along the collision axis), the shape analysis of fluorescence profiles leads directly to the angular scattering probability but experimental constraints limit the range of measurements; with a "perpendicular'' arrangement (the laser beam is perpendicular to the collision plane), fluorescence profiles are symmetrical and "forward'' contributions cannot be separated from "backward'' ones. However, extensive shape analyses have been performed with this perpendicular arrangement, since the direction of scattering was determined earlier by recording several profiles with the parallel arrangement. For the title reaction, it is shown unambiguously that, in the center of mass, CsH products scatter preferentially at small angle, in the forward direction with respect to the Cs initial velocity. The angular scattering probability varies with the collision energy but is independent of the rotational level of the product molecule (thus of its recoil velocity). These results are compatible with the harpooning mechanism which was suggested for the reaction.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 3347-3360 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The Cs(7P)+H2→CsH(X 1Σ+)(v‘=0,J‘)+H harpooning reaction has been studied in a crossed-beam experiment, with electronic excitation of Cs atoms and laser-induced fluorescence detection of CsH products performed in a coherent saturation regime. Measurements of reactive cross sections have been achieved as a function of two parameters: The collision energy Ec (0.015≤Ec≤0.15 eV) and the rotational quantum number J‘ of CsH products (0≤J‘≤16, in v‘=0). For Ec=0.09 eV, the total reactive cross sections corresponding to the two 7P fine structure levels of Cs are σ(Cs(7P1/2)+H2)=4.2×10−16 cm2 and σ(Cs(7P3/2)+H2)=10−16 cm2. These cross sections are much smaller than expected for a harpooning reaction. This is interpreted from ab initio potential energy and quantal dynamics calculations which show that the efficiency of the photochemical reaction (Cs atoms in the 7P state) is limited by the quenching processes associated with the underlying potential energy surfaces connected with Cs atoms in the 6S, 6P, 5D, and 7S states. From the present measurements, one deduces that the rate of these quenching processes is larger than 90%. The rotational distributions of products in v‘=0 measured at two collision energies (Ec=0.045 and 0.09 eV) are close to "prior'' statistical distributions, with the same "surprisal.'' The energy dependence of rotationally resolved cross sections (J‘ fixed, Ec variable) confirms the reaction thresholds and shows that there is no potential barrier higher than 0.015 eV on the entrance valley and the exit valley of the reactive system; it is in agreement with the dependence predicted by hemiquantal dynamical calculations performed in the frame of a harpooning model. The uncertainty on the measurement of absolute cross sections is larger than 70%, but of the order of 20% for relative cross sections.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 2033-2037 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We propose a new method to study metastable fragmentation of clusters in a reflectron time-of-flight mass spectrometer. This method does not require any modification of the standard apparatus. No preselection of parents is needed: all fragmentation reactions can be analyzed by recording a few numbers of spectra obtained by changing only the repelling voltage of the reflectron Vref. The evolution of a peak as a function of 1/Vref is a straight line. The extrapolation of this line at 1/Vref=0 gives the mass of the parent M and its slope gives the mass of the fragment m: the whole decay channel set for all parents can be determined unambiguously. The intensity of a peak is stable when scanning Vref: rather accurate branching ratios can be determined. Application to the fragmentation of clusters containing Ag, H2O, and SF6 is presented. Masses are measured to an accuracy of about 0.5%, allowing for example to study independently the dissociation channels involving the two natural isotopes of silver, 107Ag and 109Ag. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 6362-6367 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: NanFn−1 clusters are produced in a laser vaporization source. They are ionized by one-photon or resonant two-photon ionization, and detected in a high resolution time of flight mass spectrometer. By scanning the ionization wavelength, it is possible to obtain ionization potentials and absorption spectra of these clusters, for n ranging from 2 to 42. The results we obtain show many discrepancies with the cuboid model, which has proven valid for small sizes. The possible origin of these disagreements is discussed. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 3428-3436 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The Cs(6D3/2)+H2→CsH [X 1Σ+(v″=0,1; J″)]+H photochemical reaction has been studied in a crossed-beam experiment with electronic excitation of Cs atoms and laser-induced fluorescence detection of CsH products. The reactive cross section is measured at a collision energy of 0.09 eV: σ(6D3/2)=0.04×10−16 cm2. The rotational distributions of CsH products measured on v″=0 for 0≤J″≤23 and on v″=1 for 0≤J″≤15 are close to statistical ones with 16% of products in v″=1. A quasi-classical 3D trajectory calculation of this reaction yields both rotational and vibrational distributions of CsH products and their angular scattering probability. The reactive cross section measured with Cs(6D3/2) excitation is an order of magnitude smaller than the cross section σ(7P1/2)=0.6×10−16 cm2, which is re-evaluated in this article. © 1999 American Institute of Physics.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 14 (2001), S. 323-330 
    ISSN: 1434-6079
    Keywords: PACS. 36.40.Qv Stability and fragmentation of clusters
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: The abundance spectra and the fragmentation channels of silver bromide clusters have been measured and analyzed. The most abundant species are AgnBrn - 1 + and AgnBrn + 1 - and Ag14Br13 + is a magic number, revealing their ionic nature. However, some features depart from what is generally observed for alkali-halide ionic clusters. From a certain size, AgnBrn - 1 + is no more the main series, and AgnBr n - 2, 3 + series become almost as important. The fast fragmentation induced by a UV laser makes the cations lose more bromine than silver ions and lead to more silver-rich clusters. Negative ions mass spectra contain also species with more silver atoms than required by stoichiometry. We have investigated the metastable fragmentation of the cations using a new experimental method. The large majority of the cations release mainly a neutral Ag3Br3 cluster. These decay channels are in full agreement with our recent ab initio DFT calculations, which show that Ag+-Ag+ repulsion is reduced due to a globally attractive interaction of their d orbitals. This effect leads to a particularly stable trimer (AgBr)3 and to quasi-planar cyclic structures of (AgBr)n clusters up to n = 6. We have shown that these two features may be extended to other silver halides, to silver hydroxides (AgOH)n, and to cuprous halide compounds.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 28 (2004), S. 361-366 
    ISSN: 1434-6079
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. This paper describes the spectroscopy of Na3F both in the frequency and time domains. The photoionization efficiency curve shows two thresholds, associated to two isomers. The excited electronic states of the C2v isomer have been probed by photodepletion spectroscopy, and the results are used to analyze a time-resolved study of photoexcited Na3F, probed by photoionization. The pump-probe signal clearly shows damped oscillations, the period of which is fitted to $390\pm10$ fs, close to twice the previously measured bending mode of Na2F [1], while the relaxation time is $1275\pm50$ fs.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 34 (1995), S. 135-138 
    ISSN: 1434-6079
    Keywords: 71.50.+t ; 36.40.+d
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The temperature of a sodium fluoride cluster beam produced by laser vaporization is estimated from the rotationally-resolved laser spectroscopy of the Na2 dimer. The cluster beam is obtained by laser vaporization of a sodium rod in a mixture of helium containing a small amount (1%) of SF6. Both rotational and vibrational temperatures (respectively 170 K and 400 K) are much higher than expected from a simple theoretical model of a supersonic beam. These temperatures can be lowered to 70 K and 250 K respectively by cooling the nozzle to liquid nitrogen temperature.
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