Rotationally Inelastic Diffraction Research Articles

Experimental and theoretical study of rotationally inelastic diffraction of H2(D2) from methyl-terminated Si(111).

Fundamental details concerning the interaction between H2 and CH3-Si(111) have been elucidated by the combination of diffractive scattering experiments and electronic structure and scattering calculations. Rotationally inelastic diffraction (RID) of H2 and D2 from this model hydrocarbon-decorated semiconductor interface has been confirmed for the first time via both time-of-flight and diffraction measurements, with modest j = 0 → 2 RID intensities for H2 compared to the strong RID features observed for D2 over a large range of kinematic scattering conditions along two high-symmetry azimuthal directions. The Debye-Waller model was applied to the thermal attenuation of diffraction peaks, allowing for precise determination of the RID probabilities by accounting for incoherent motion of the CH3-Si(111) surface atoms. The probabilities of rotationally inelastic diffraction of H2 and D2 have been quantitatively evaluated as a function of beam energy and scattering angle, and have been compared with complementary electronic structure and scattering calculations to provide insight into the interaction potential between H2 (D2) and hence the surface charge density distribution. Specifically, a six-dimensional potential energy surface (PES), describing the electronic structure of the H2(D2)/CH3-Si(111) system, has been computed based on interpolation of density functional theory energies. Quantum and classical dynamics simulations have allowed for an assessment of the accuracy of the PES, and subsequently for identification of the features of the PES that serve as classical turning points. A close scrutiny of the PES reveals the highly anisotropic character of the interaction potential at these turning points. This combination of experiment and theory provides new and important details about the interaction of H2 with a hybrid organic-semiconductor interface, which can be used to further investigate energy flow in technologically relevant systems.

On the influence of incident angle in the scattering dynamics of D 2 from NiAl(1 1 0)

The scattering dynamics of D 2 from NiAl(1 1 0) has been investigated both experimentally and theoretically. Diffraction and rotational transitions of D 2 from NiAl(1 1 0)[1 1 ̄ 0] have been measured at incident energies between 88 and 157 meV. The measurements were done using a setup which allows recording of diffraction patterns at a fixed angle of incidence. Elastic first-order diffraction and rotationally inelastic diffraction (RID) peaks were resolved over the whole incident energy range studied. The 0→2 transition probability was found to be about a factor of 2 higher than the one reported on Cu(0 0 1), whereas the 2→0 transition remained constant in the energy range investigated. Concerning the two rotational transition probabilities observed in experiment, one major conclusion of our work is that the behaviour they exhibit as a function of incident energy is independent of angle of incidence. All these observations are well reproduced by ab initio quantum mechanical calculations.

Isotope effects on the rotationally inelastic diffraction dynamics of hydrogen scattered from Cu([formula omitted

We investigate the rotationally inelastic diffraction (RID) of D2(H2) scattered from Cu(001) and discuss how isotope effects influence the RID probabilities of D2(H2) by performing quantum dynamics calculations that include all six degrees of freedom of D2(H2). We show that the RID probabilities initially increase with increasing incident energies due to the activated nature of D2(H2) dissociation on Cu(001), which qualitatively agree with recent experimental RID peaks measured for D2/Cu(001). Furthermore, comparing the RID probabilities of D2 and H2, we observed strong isotope effects. Due to the small threshold energy of D2 for rotational excitation and diffraction, as compared to H2, the RID probabilities of D2 are larger than those of H2 in the low incident energy region. However with further increase in incident energies, the RID probabilities of D2 become smaller than those of H2. We conclude that this is a manifestation of the steering effect in the RID.

固体表面での水素分子の回転励起を伴う回折現象

We investigate the rotationally inelastic diffraction (RID) of D2(H2) scattered from Cu(001) and discuss how isotope effects influence the RID probabilities of D2(H2) by performing First Principles Quantum Dynamics Calculations that include all six degrees of freedom of D2(H2) on a density functional theory based potential energy surface. We show that the RID probabilities initially increase with increasing incident energies due to the activated nature of D2(H2) dissociation on Cu(001), which qualitatively agree with recent experimental RID peaks measured for D2/Cu(001). Furthermore, comparing the RID probabilities of D2 and H2, we observe strong isotope effects. Due to the small threshold energy of D2 for rotational excitation and diffraction, as compared to H2, the RID probabilities of D2 are larger than those of H2 in the low incident energy region. With further increase in incident energies, however, the RID probabilities of D2 become smaller than those of H2. We explain these isotope effects on the RID by showing the wave functions of D2(H2) on Cu(001).

Diffraction and rotational transitions in the scattering of D2 from Cu(001) at energies up to 250 meV

Absolute diffraction probabilities for the scattering of D2 from a clean Cu(001) surface along the [100] azimuth have been measured at incident kinetic energies between 20 and 250 meV. The measured attenuation of the diffraction intensities with surface temperature corresponds to a surface Debye temperature of ΘD=341 K. The high-resolution angular distributions show clear evidence of rotationally inelastic diffraction (RID) peaks. The RID probability increases with incident energy and represents as much as 30% of the elastic diffraction probability at energies above Ei=200 meV. An Eikonal approximation analysis gives a value h=0.075 Å for the surface corrugation which is independent of incident energy. The rotational transition probabilities correspond to an effective value of δ=0.3 for the molecular eccentricity. The experimental results indicate that diffraction of D2 from Cu(001) can be accounted for by a hard-wall collision mechanism over the whole range of investigated energies.