The He–N<sub>2</sub>anisotropic Van der Waals potential. Test of a simple model using state-to-state differential scattering cross-sections

Faubel, Manfred; Kohl, K. H.; Toennies, J. P.; Tang, Kwong Tin; Yung, Y. Y.

doi:10.1039/dc9827300205

Cited by 91 publications

(10 citation statements)

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“…In our previous work [14] on N2-He we found that for the interaction second virial coefficients, the shear viscosity and binary diffusion coefficients, the HFD1 surface was the only one to predict values within most of the experimental error bars. However, for the same system, neither of the HFD1 or HFD2 surfaces agreed well with the total differential collision cross section data of Faubel et al [55], but both gave results that agreed reasonably well with the inelastic state-tostate differential collision cross sections [55]. At the moment, it seems that no single currently available recipe for determining the anisotropic damping factor p(y) is adequate for obtaining accurate HFD potential energy surfaces for such systems.…”

Section: Discussionmentioning

confidence: 61%

New anisotropic potential energy surfaces for N₂-Ne and N₂-Ar

et al. 1987

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New anisotropic potential energy surfaces of the Hartree-Fock plus damped dispersion (HFD) type have been obtained for the N2-Ne and N2-Ar interactions. The SCF energies utilized in constructing the short-range part of the interactions were computed at 20 points on each surface by using basis sets of double zeta plus polarization quality. Anisotropic C 6 and Cs dispersion coefficients, utilized in constructing the long-range part of the interaction, have been calculated with a recently obtained combining rule. Several procedures are introduced for estimating the anisotropic damping factors used in the description of the correlation energy contributions in the HFD model. The essential differences amongst the surfaces reported here arise from these estimates. Comparisons are made with other available anisotropic N2-Ne and N2-Ar surfaces. The predictive ability of all surfaces with respect to the temperature dependence of the interaction second virial coefficient, BI2(T ), has also been tested. For the N2-Ne system only the present HFD3 surface gives good agreement with the experimental interaction second virial coefficients over a wide temperature range. Similarly, for the Nz-Ar system the surface of Candori et al. [1983, Chem. Phys. Lett., 102, 412], which was partially determined using the second virial coefficient data, and the present HFD1 surface give good agreement with experimental virial data.

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Section: Discussionmentioning

confidence: 61%

New anisotropic potential energy surfaces for N₂-Ne and N₂-Ar

et al. 1987

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“…9 The cross section falls off rapidly by several orders of magnitude over an angular range of a very few degrees, after which it flattens out and becomes marked by oscillations, which have been attributed to Fraunhofer shadow diffraction from the hard core of the potential. 10 Fraunhofer diffraction has been observed for many systems in He-molecule scattering and has been shown to provide a sensitive measure of the distance at which the repulsive and attractive forces just cancel each other. 11 At even larger angles molecular scattering is dominated by the hard-core repulsive potential.…”

Section: Observation Of Interference Oscillations In Helium Scatterinmentioning

confidence: 99%

Observation of Interference Oscillations in Helium Scattering from Single Surface Defects

Lahee¹,

Manson²,

Toennies³

et al. 1986

Phys. Rev. Lett.

117

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Large-angle-diffraction oscillations in the intensity of helium atoms elastically scattered from randomly stepped Pt(lll) are reported. A formalism based on the concept of reflection-symmetry interference explains the observed features and the data analysis yields a value of 4.4-4.6 A for the hard-core repulsive cross section of a single step. The observed oscillations are sensitive to the presence of adsorbates at step sites.PACS numbers: 79.20. Rf, 61.16.Fk, 6L70.Ey, 68.35.Dv There is now considerable evidence that surface defects (steps, kinks, and point defects) provide the active sites for chemical reactions on single-crystal surfaces. 1 LEED provides the present standard technique for determining defect geometries and densities, 2 but to date its sensitivity has only been sufficient to study the statistical distribution of defects and not their individual details. The angle or energy dependence of the specular scattering of He atoms has been shown to provide quantitative information on step heights and average densities, 3 and more recently the attenuation of the specular beam in He atom scattering by steps has been demonstrated. 4 Since the integral total cross sections derived in the latter type of measurement are dominated by long-range attractive forces, they are rather large (= 12 A) (Ref. 4) and consequently do not provide direct details on the physical size or orientation of the steps, nor on changes in the immediate environment of the single steps as may occur during gas adsorption. In this Letter, we report on the first observation of large-angle hard-core diffraction from single randomly spaced monatomic steps on a single crystal surface, in this case Pt(lll). Since the observed diffraction patterns are determined by the interference of atom trajectories probing the repulsive potential of the step and the adjacent undisturbed smooth mirrorlike regions, the actual size and orientation of the single steps could be determined. We also see striking changes in the step diffraction as CO is adsorbed at the steps, demonstrating that valuable chemical information on active sites in heterogeneous catalysis can be obtained by this new technique.The observation of diffraction from single steps has been made possible by the introduction of highresolution He nozzle beams and sensitive time-offlight detection techniques used to study surface phonons. 5 The apparatus is essentially identical to that used in the phonon studies; however, in the present experiment only the elastic peak is of interest. The helium beam energy can be varied between 8 and 80 MeV (/c/ = 4-12.7 A"" 1 ) with a velocity resolution Av/v of 1%. The polished Pt (111) crystal was cleaned in vacuum (base pressure 10"" 10 Torr) by cycles of sputtering, annealing at 1000 K, and heating in oxygen until no impurities were detected in the Auger trace. In most of the experiments the sum of incident 0, and final angles B f is 90°. The parallel momentum transfer, AJ£= B fc/(sin0/--sin0/), is varied by rotation of the crystal in the scattering plane ...

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“…From a "near-side/far-side" analysis 15 of state-to-state differential cross sections as functions of the center-of-mass scattering angle, Stoecklin et al 13 have shown that the available data, 16,17 which span scattering energies of 220-250 cm −1 , are only marginally able to distinguish among the semiempirical XC͑fit͒ PES of Ref. 8 and the ab initio ͑"MTE" and BCCD͒ PESs of Refs.…”

Section: Introductionmentioning

confidence: 99%

Predicted bound states and microwave spectrum of N2–He van der Waals complexes

Roy

McCourt

2009

The Journal of Chemical Physics

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Numerical calculations show that four modern potential energy surfaces for N(2)-He all support 18 bound intermolecular states for the homonuclear isotopologues (14,14)N(2)-(4)He and (15,15)N(2)-(4)He, and 12 (or 13, for one surface) truly bound states for (14,15)N(2)-He. This contradicts a recent statement [Patel et al., J. Chem. Phys. 119, 909 (2003)] that one of these surfaces supports no bound states, and it yields predictions for 27 allowed pure rotational transitions among the truly bound states of the homonuclear isotopologues of this complex.

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The He–N₂anisotropic Van der Waals potential. Test of a simple model using state-to-state differential scattering cross-sections

Cited by 91 publications

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New anisotropic potential energy surfaces for N₂-Ne and N₂-Ar

New anisotropic potential energy surfaces for N₂-Ne and N₂-Ar

Observation of Interference Oscillations in Helium Scattering from Single Surface Defects

Predicted bound states and microwave spectrum of N2–He van der Waals complexes

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The He–N2anisotropic Van der Waals potential. Test of a simple model using state-to-state differential scattering cross-sections

Cited by 91 publications

References 0 publications

New anisotropic potential energy surfaces for N2-Ne and N2-Ar

New anisotropic potential energy surfaces for N2-Ne and N2-Ar

Observation of Interference Oscillations in Helium Scattering from Single Surface Defects

Predicted bound states and microwave spectrum of N2–He van der Waals complexes

Contact Info

Product

Resources

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The He–N₂anisotropic Van der Waals potential. Test of a simple model using state-to-state differential scattering cross-sections

New anisotropic potential energy surfaces for N₂-Ne and N₂-Ar

New anisotropic potential energy surfaces for N₂-Ne and N₂-Ar