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  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 6698-6708 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The dynamics of the reactions O(1D)+H2→OH+H and O(1D)+D2→OD+D have been investigated in crossed molecular beam experiments with mass spectrometric detection at the collision energies of 1.9 and 3.0 kcal/mol, and 5.3 kcal/mol, respectively. From OH(OD) product laboratory angular and velocity distribution measurements, center-of-mass product translational energy and angular distributions were derived. The angular distributions are nearly backward–forward symmetric with a favored backward peaking which increases with collision energy. About 30% of the total available energy is found to be channeled into product translational energy. The results are compared with quasiclassical trajectory calculations on a DIM (diatomic-in-molecules) potential energy surface. Related experimental and theoretical works are noted. Insertion via the 1 1A′ ground state potential energy surface is the predominant mechanism, but the role of a second competitive abstraction micromechanism which should evolve on one of (or both) the first two excited surfaces 1A″ and 2 1A′ is called into play at all the investigated energies to account for the discrepancy between theoretical predictions and experimental results. © 1998 American Institute of Physics.
    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 110 (1999), S. 8857-8860 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In the first successful reactive scattering study of nitrogen atoms, the angular and velocity distribution of the ND product from the reaction N(2D)+D2 at 5.1 and 3.8 kcal/mol collision energies has been obtained in a crossed molecular beam study with mass spectrometric detection. The center-of-mass product angular distribution is found to be nearly backward–forward symmetric, reflecting an insertion dynamics. About 30% of the total available energy goes into product translation. The experimental results were compared with those of quasiclassical trajectory calculations on an accurate potential energy surface obtained from large scale ab initio electronic structure computations. Good agreement was found between the experimental results and the theoretical predictions. © 1999 American Institute of Physics.
    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 116 (2002), S. 5603-5611 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The reaction between atomic carbon and acetylene has been investigated using complementary crossed molecular beam techniques. Differential cross sections have been obtained for the reactions of both ground and excited carbon atoms, C(3PJ, 1D2)+C2H2(X 1Σg+), in experiments conducted with continuous supersonic beams, mass spectrometric detection, and time-of-flight analysis at a relative translational energy of 29.3 kJ mol−1. The reaction C(3PJ)+C2H2(X 1Σg+) has been found to lead to C3H+H and C3+H2 products in comparable amounts. Both H and H2 elimination pathways are found to proceed through the formation of a C3H2 long-lived intermediate complex whose lifetime may be comparable to its rotational period. The spin-forbidden H2 elimination channel is attributed to the occurrence of intersystem-crossing between the triplet and singlet manifolds of the C3H2 potential-energy surfaces. The reaction C(1D2)+C2H2(X 1Σg+) has been found to lead to formation of C3H+H, with a C3H center-of-mass angular distribution strongly forward peaked, indicating a short-lived intermediate complex. Integral cross sections have been obtained for the C(3PJ)+C2H2(X 1Σg+)→C3H+H(2S1/2) reaction in experiments conducted with pulsed, supersonic molecular beams in the range of relative translational energies ET=0.38−25.5 kJ mol−1, the H(2S1/2) product being detected by laser-induced fluorescence. The reaction has been found to be without a barrier, relative integral cross sections being proportional to (ET)−0.80±0.03 below ET=10 kJ mol−1. These findings provide direct evidence that the C(3PJ)+C2H2 reaction can occur under the physical conditions prevailing in dense interstellar clouds and, in particular, that it may be the source of both C3H and C3 species in these extreme environments. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 5827-5845 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A detailed comparison of the predictive powers of two recently determined empirical and two recently proposed theoretical potential energy surfaces for the N2–He interaction has been carried out. In particular, the following properties have been tested: at the microscopic level, total and state-to-state differential cross sections and absolute total integral cross sections, while at the macroscopic level, interaction second virial, diffusion, viscosity, and thermal conductivity coefficients, as well as the rotational relaxation time, depolarized Rayleigh spectral collision broadening, and shear viscosity and thermal conductivity field-effect data in N2–He mixtures. Exact calculations have been employed, from the close-coupling method for treating scattering data at low energies to the classical trajectory method with second-order corrections to compute the effective cross sections that determine the bulk transport and relaxation phenomena.The empirical exponential-spline–Morse-spline–van der Waals surface [J. Chem. Phys. 85, 7011 (1986)], closely followed by the model Bowers–Tang–Toennies surface [J. Chem. Phys. 88, 5465 (1988)], gives better simultaneous agreement with the scattering data, the second virial coefficient data, the bulk transport data, and the depolarized Rayleigh collision-broadening data, which are properties sensitive to the spherical component of the interaction and to the anisotropy of the low repulsive wall. None of the potential surfaces examined here includes a dependence upon the vibrational stretching coordinate of the N2 molecule, since none of the data employed in the fitting is sensitive to this coordinate. The two theoretical model potentials, especially that based upon an earlier Hartree–Fock plus damped dispersion model surface [J. Phys. Chem. 88, 2036 (1984)], gives better agreement with the rotational relaxation and field-effect data, which are properties sensitive to the anisotropy of the high-repulsive wall. It is established that the exponential-spline–Morse-spline–van der Waals and Bowers–Tang–Toennies surfaces are on the whole the more reliable of the empirical and model surfaces examined, respectively. It is concluded that the optimum N2–He potential energy surface should be a blend of the empirical exponential-spline–Morse-spline–van der Waals and of the two model surfaces.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The full anisotropic potential energy surface for the Ne–O2 van der Waals molecule has been obtained from the simultaneous analysis of total differential cross section data with well resolved diffraction oscillations and of absolute total integral cross section data with glory structure measured in Perugia, of the Zeeman spectrum measured in Nijmegen, and of transport coefficients taken from literature. The anisotropy of the interaction is obtained from the Zeeman spectrum using both numerical and analytical approaches for the energy levels, and from the quenching of the diffraction oscillations in the total differential cross section within the infinite-order-sudden approximation. The latter approximation is practically exact under the experimental conditions, as previously shown for the similar Ne–N2 system by comparison with exact close-coupling scattering calculations. The derived potential energy surface represents a dramatic improvement with respect to a previous approximate estimate.
    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 94 (1991), S. 8611-8614 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Crossed beam reactive scattering studies of the H displacement reaction of both ground 3P and excited 1D oxygen atoms with H2S show that the reaction dynamics changes dramatically upon electronic excitation: while the reaction of O(3P) is direct, that of O(1D) proceeds via a long-lived complex.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: High-resolution crossed molecular beam measurements of the total differential cross section (DCS) for the scattering of Ne by N2 at a collision energy of E=75.8 meV are reported. Strongly quenched diffraction oscillations superimposed on the falloff of the main rainbow structure are clearly resolved. A reliable Ne–N2 potential energy surface (PES) is derived by simultaneously fitting second virial, diffusion, and viscosity coefficient data taken from the literature. Information on the anisotropy of the interaction is obtained from the quenching of the diffraction oscillations in the total DCS within the framework of the infinite-order-sudden (IOS) approximation. The reliability of the IOS approximation in deriving a fully anisotropic potential energy surface from the measured scattering dynamics is examined and demonstrated by performing exact close-coupling calculations for the present experimental conditions and then comparing both integral and differential total and rotationally inelastic cross sections. The derived PES is compared with recently proposed theoretical model potential surfaces. Although in satisfactory agreement with bulk properties, none of these surfaces predicts correctly the present scattering data, each having significantly different spherical and/or anisotropic components in comparison with the PES derived here.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 4671-4679 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The anisotropic potential energy surface of He–CO2 is determined by the simultaneous analysis of newly measured high resolution total differential cross sections, differential energy loss spectra, new low temperature second virial coefficients, new diffusion, and viscosity data. The calculations are carried out in the infinite-order-sudden approximation. The repulsive anisotropy of the potential is determined from the rotationally inelastic cross sections and the quenching of the diffraction oscillations, while the absolute scale is fixed by the position of these oscillations. The second virial coefficient data are essentially sensitive to the general features of the spherical effective potential well. The transport data are then correctly predicted by this potential surface which differs both in the anisotropy and the spherical part from the recently derived multiproperty fit potential for this system.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 7926-7939 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A new multiproperty potential energy surface for the N2–Ar intermolecular interaction is reported. The present determination is based upon molecular beam total differential and integral scattering data, taken together with the temperature dependence of the interaction second virial coefficient, transport properties, transport property field effects, and relaxation phenomena, such as pressure broadening of the depolarized Rayleigh line and longitudinal nuclear spin relaxation. The primary fit has been made to the beam scattering and virial data, and refinements to the potential parameters thus determined have been made by employing the data available for the gas phase transport and relaxation phenomena. The potential energy surface employed is an empirical Morse–Morse–spline–van der Waals form, in which the potential parameters depend upon the angle between the N2 figure axis and the line joining the centers of mass of N2 and Ar. No N2 stretching dependence has been included in the present determination. Comparison is made between the present potential energy surface and two other previously published N2–Ar potential energy surfaces. The present potential energy surface provides the best overall agreement for all available gas phase data for N2–Ar mixtures, and can thus be recommended for calculations of all properties of such mixtures that depend upon the intermolecular interaction.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Journal of the American Chemical Society 106 (1984), S. 4108-4111 
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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