Orientation and bonding of adsorbed CH3NCO on Pt{110} and Cu{110} from vibrational and photoelectron spectroscopies

The bonding and orientation of CH{in3}NCO on Pt{110} and Cu{110} are studied by HREELS, ARUPS, AES, and LEED. CH{in3}NCO is found to adsorb nondissociatively on both Cu{110} and Pt{110} at T = 160 K, bonding primarily through the 2π a′ orbital with the NCO group lying down on the surface and the methyl group largely unperturbed. We propose that the absence of a strong HREELS band at about 2290 cm^?1, which is the liquid phase frequency for the NCO asymmetric stretching mode, combined with the presence of strong bands between 1000 and 1450 cm^?1 provides a “finger-print” for NCO bonded to the surface in a lying-down configuration.     

Thermal roughening of FEM-clean Pt{110} and its vicinal areas

After heat treatment at ∼1600 K and rapid quenching, thermal roughening through kink formation could be observed on “FEM-clean” Pt{110} and on all its vicinal areas (which are made up of {110} terraces). Noticeable exceptions were the areas between {771} and {331} (including {771}), which are located on the [1̄10] zone. These areas may remain topographically unchanged, or, more likely, may form {111}-microfacets during heat treatment. Upon annealing, the high-temperature roughness on {110} started to decrease at 830 K (formation of an 1 × 2 structure) and reached a minimum at 960 ± 25 K (≡ transition temperature, T_c). Thereafter, it increased precipitously until 1030 K was reached (surface roughening/deconstruction). Surface roughening could be suppressed readily by gas phase and/or bulk impurities (surface segregation). Vapour deposited Si, P, SiO, TiO₂, Al₂O₃ and C (graphite) prevented surface roughening on Pt{110}. All investigations were carried out by FEM.     

Nucleation and orientation of graphite{0001} layers on Pt{110}

Investigations by field electron microscopy revealed that graphite{0;0001} layers grow preferentially on Pt{110}. Layer nucleation and initial growth occurs in the vicinal area of {110} along the 〈112〉 and the 〈100〉 zones and not on the unstepped {110} plane itself. The growth rate in the vicinal area is determined by the epitaxial misfit parallel to the step edges. An alignment of the graphite layer with the underlying {110} is observed. It corresponds to graphite〈101̄0〉 ∥ Pt〈100〉, which coincides with the calculated orientation of smallest epitaxial misfit. The change of relative emission from {110} upon adsorption of graphite is discussed.     

Diffusion processes of trimers on missing row surfaces: \mathrm{Cu }_{3}/\mathrm{Ag }(110) and \mathrm{Ag }_{3}/\mathrm{Cu }(110)

A semi-empirical potential according to the embedded atom, has been applied to investigate the diffusion of trimers by computing the energy barriers for different mechanisms. Our attention was more focused on the leapfrog process which is likely to occur on missing row surfaces. The activation barriers of this mechanism are calculated using drag method at 0K. These barriers are found to be 0.64 and 0.68 eV for hopping out the channel for $\mathrm{Cu }_{3}/\mathrm{Ag }(110) \mathrm{and Ag }_{3}/\mathrm{Cu }$ (110) respectively. While for hopping down at the other side they are about 0.42 and 0.32 eV. Moreover, a deep metastable position is observed during leapfrog diffusion leading to some spectacular trimer motion. At high temperature and essentially for $\mathrm{Cu }_{3}/\mathrm{Ag }$ (110), we also observed a competition between leapfrog process and concerted jump mechanism with a deformation of trimer geometry. Implications of these findings are briefly discussed.     

Resonance photoelectron spectroscopy from autoionization states of CH3I

Resonance photoelectron spectra of methyl iodide have been taken by exciting individual autoionizing Rydberg states, and measuring the ejected electron energies by a time of flight technique. A number of spectra were obtained from autoionization states which are members of two series, converging respectively to the ²E_{$\text{1}\text{2}$} (ν = 0) and ²E_{$\text{1}\text{2}$} (ν₂ =1) states of the ion. In addition to observing vibrational bands not previously reported, we found that the peak intensities are consistent with Bardsley's formulation of the configuration interaction theory of autoionization.     

Orientation of chemisorbed species from orthogonal-plane arups: Tilted CO on Pt{110} and upright CO on Pt{111}.

Angle-resolved photoemission spectra obtained with electron collection in the plane orthogonal to the incidence plane, using a He II photon source, are used to provide an accurate measure of the orientation of chemisorbed diatomic molecules. As previously established, CO in the Pt{111}c(4 × 2) structure is found to be chemisorbed in an upright configuration, whereas in the Pt{110}(2 × 1) p1g1 structure the CO molecular axis is tilted 26 ± 2° away from the surface normal, in a direction between [211] and [433].     

Observation of occupation and dispersion of 2π1 associated states for CO adsorbed on Cu{100}

Angle-resolved photoemission observations of CO adsorbed on Cu{100} to form the (√2 × √2)R45° structure show emission from a CO 2π¹ related state away from the centre of the surface Brillouin zone. These observations are shown to be compatible with the anticipated dispersion of such states and with weak 2π¹ backbonding on this substrate.     

Rotational spectrum of acetonitrile CH3CN and CH3CN in a doubly excited degenerate vibrational state

The rotational spectrum of the acetonitrile molecules CH₃C¹⁴N and CH₃C¹⁵N in the degenerate vibrational state v₈ = 2 has been studied for the transitions J = 0 → 1, 2 → 3, 3 → 4, 4 → 5, 5 → 6, 6 → 7, and 7 → 8.     

Pressure-induced ferroelectricity in {N(CH3)4}2FeCl4

The hydrostatic pressure effect on the stability of phases I, II, III and IV in {N(CH₃)₄}₂FeCl₄ was studied by dielectric and DTA measurements in the temperature and pressure region of -40-30°C and 0–2 kbar. The pressure-induced new phase V found at applied pressures between 0.3 and 1.0 kbar was confirmed to be ferroelectric by the observation of D-E hysteresis loop. These results are compared with those of {N(CH₃)₄}₂XCl₄ (X: Co, Zn and Mn) in this paper.     

Adsorption parameters of Cu and Ni on the {110} plane of W and Mo

This paper reports on the embedded-atom method (EAM, developed by Johnson) calculations of adsorption parameters for Cu and Ni on {110} unrelaxed substrates of Mo and W. The following are calculated: (i) the equilibrium height h _c of an adatom; (ii) the optimum coefficients W ₀ A _hk of a truncated Fourier representation of the adatom-substrate interaction potential; (iii) the desorption energies E _des ; and (iv) the activation energies Q of surface migration. It is shown that (a) the calculated values of E _des agree satisfactorily with available empirical data; (b) the scale factor W ₀ is approximately proportional to the bonding as measured by E _des , whereas the normalized coefficients A _hk are determined by the {110} substrate symmetry; (c) E _des and Q are respectively dominated by the embedding energy and pair potential of the EAM; and (d) W ₀ and E _des for an atom in a monolayer are only about half as much as the corresponding quantities for an isolated atom.     

Orientation of chemisorbed species from electron impact and dipole selection rules: The formate ion on Pt{110}

Selection rules in high resolution electron energy loss spectroscopy are shown to permit a determination of the structure of formate ions adsorbed on Pt{110} from data obtained on and off specular along three different azimuthal directions. Long-range dipole scattering indicates that the ion is adsorbed upright bonding, through the two oxygen atoms. Shorter-range impact scattering provides the further information that the ion is coplanar with the 〈110〉 direction and tilted (in the same plane) through at most 10^° from the surface normal.     

A synchrotron radiation study of the electronic and geometric structure of CO on Pt{110}

Using both synchrotron and HeII radiation the electronic and geometric structure of Pt{110}-(2×1)p1g1 CO was examined. The shape resonance for the 4σ orbital of CO is found to be peaked at 38 eV, while that for the 5σ orbital is peaked at 28 eV. No shape resonance is observed from the 1π orbital. The $\text{5σ}\text{1π}$ ordering is reversed from that of gas phase CO. Further evidence, from the polar intensity variation of the non-bonding 4σ orbital, is presented for the tilted CO structure proposed previously.     

Spin texture and circular dichroism in photoelectron spectroscopy from the topological insulator bi_{2}te_{3}: first-principles photoemission calculations

By relativistic first-principles photoemission calculations for the topological insulator Bi_{2}Te_{3}, we study how the spin texture of the Dirac state manifests itself in circular dichroism. On one hand, there are significant modifications of the initial state's spin texture, which are explained by final-state effects and the symmetry of the photoemission setup. On the other hand, a highly symmetric setup allows us to draw conclusions about the detailed Dirac state's spin texture. Our study supports that circular dichroism in angular distribution successfully complements spin- and angle-resolved photoelectron spectroscopy from topological insulators.     

New ground state constants of CH3Cl and CH3Cl from global polyad analysis

A global analysis of the infrared spectrum of chloromethane involving the ground state and the 13 vibrational states lying up to 2600 cm⁻¹ was recently achieved using high resolution Fourier transform spectra of pure isotopomers. More than 20 000 transitions (cold and hot bands) for each isotopomer ¹²CH₃³⁵Cl and ¹²CH₃³⁷Cl have been assigned and fitted with a standard deviation of about 3 × 10⁻⁴ cm⁻¹ close to the experimental precison. As part of this global effort, improved ground state constants up to sextic centrifugal distortion terms have been determined for each isotopomer taking advantage of the numerous allowed and perturtation-allowed transitions simultaneously fitted using our global model. The axial constants could be determined from ΔK ≠ 0 combinations arising from rovibrational local resonances within Polyads 3 and 5.