Polarization of out-of-plane scattering from microrough silicon

The polarization of light scattered by silicon with a small degree of microroughness was measured out of the plane of incidence. First-order vector perturbation theory for scattering from a rough surface predicts the behavior well. The data and the theory show Brewster-like angles where p?p scattering from surface microroughness vanishes, as well as a deterministic polarization in other directions.     

An out-of-plane force field for p-benzoquinone and some structurally related molecules

A simplified out-of-plane valence force field in the harmonic approximation has been constructed for ethene, butadiene, glyoxal, acrolein, and p-benzoquinone using the overlay technique. p-Benzoquinone is considered to consist of two conjugated OCCHCHCO systems and force constants from the first four mentioned molecules are shown to be successfully transferable to p-benzoquinone. The force field has 21 independent parameters and gives a root-mean-square frequency error of 7.61 cm^?1.     

Angular distribution of EELS intensities: CO on Pt(111)

We present the angular distribution of inelastic intensities corresponding to the excitation of the vibrational modes of CO chemisorbed on Pt(111). The experimental values are compared with those predicted by dipole scattering. All the vibrational modes, including the C-metal, stretch, show experimental values larger than theoretical ones. The difference is attributed to vibrational excitation by impact scattering. The impact scattering cross section is found to be energy dependent and increases for low primary energies (2 eV). The differential cross section is, however, smaller than that observed for resonant scattering in free CO.     

Determination of an energy distribution from stopping potential data

The energy spectrum of electrons just inside an irradiated surface is obtained in terms of the derivatives of the current—voltage curve for electrons emitted from the surface. For the familiar case of a unidirectional beam, the energy distribution is just the negative of the first derivative. For an (assumed) isotropic distribution inside the surface, a classical surface potential, and a spherically symmetric retarding field, the energy distribution is similar to the unidirectional case except that the first derivative must be multiplied by an energy-dependent factor. If the retarding field is uniform and perpendicular to the surface, the calculation of the energy distribution inside involves both the first and second derivatives.     

Raman intensities of methanes from electrooptical parameters

This paper deals with the calculation of the intensities of Raman active fundamental vibrations of methane and its isotopical derivatives by the electrooptical theory of valence and with the “least squares” refinement of a set of electrooptical parameters from the experimental data. First some general considerations on the electrooptical theory of valence and on the computational method are presented. Then we give the expressions of the Raman intensities and depolarization ratios as functions of the electrooptical parameters and discuss some features of the “least squares” refinement technique. The results of our calculations on methane and deuteroderivatives are then reported. Particular attention has been given to the study of the type and combinations of parameters affecting each intensity.     

The steady state out-of-plane response of an internally damped ring supported by springs in some bays

The steady state out-of-plane response of an internally damped ring supported by springs in some bays to a sinusoidally varying point force or moment is determined by use of the transfer matrix technique. For this purpose, the equations of out-of-plane vibration of a uniform circular ring based upon the Timoshenko beam theory are written as a coupled set of first order differential equations by using the transfer matrix of the ring. The matrix is obtained analytically and the steady state response of the ring is determined by the product of the matrices in free bays and those in supported bays. In this case, the elastic moduli of the ring and springs with internal damping are assumed to be complex quantities. The method is applied to rings supported against deflection and torsion in some bays of the same length located at equal angular intervals; the driving point impedance, transfer impedance and the distributions of the deflection, angular rotation, force and moment are calculated numerically, and the effects of the number, the stiffness and the length of supporting springs on them are studied.     

Evaluation of critical exponents from raman intensities

Theory and experiment are compared for Raman intensities near continuous structural phase transitions. Situations in which the order parameter couples linearly to light or quadratically are considered. Both cases are easily analyzed for the soft modes in ferroelastic LnP₅O₁₄ (Ln = La, Pr, Nd, Tb). The trace polarizability tensor yields β = 0.49 ± 0.02; off-diagonal terms give γ’ = 1.16 ± 0.15 and γ = 1.07 ± 0.10. Mean field results are also obtained for barium sodium niobate near T (incommensurate) = 582 K and for tris-sarcosine calcium chloride near T _c = 128 K.     

Determination of the distribution of steps on a surface from LEED spot profiles

Within the kinematic approximation, the LEED profile from a one-dimensional stepped surface can be approximately expressed as a sum of Lorentzians and δ-functions for an arbitrary step distribution. Especially for the geometric and Γ-distributions, this expression is exact. The peak positions and widths of the Lorentzians are directly related to the step distribution. For this reason, a direct estimate of the step distribution by fitting a measured LEED profile becomes possible.     

Determination of some transport properties of argon from transient arc behaviour

A new method is described which enables the electrical conductivity and electron mobility to be derived from the measurement of either the decay, following interruption, or response of a wall stabilized arc to a step change in current. This has been achieved by using a laser interferometer to record the corresponding change in electron density. The method has been applied to arcs of different radii and the derived transport properties are given in the range 8,800–12,200 °K for argon at atmospheric pressure.     

Determining the energy distribution function of electrons in the negative-luminescence plasma of a glow discharge from the line intensities

The energy distribution function of electrons (EDFE) in the negative luminescence of a glow discharge is found using, as well as the probe method, calculation from measured spectralline intensities. The measurements are made in a weakly anomalous discharge in helium at a pressure of 0.5 mm Hg. In the energy range from 0 to 35 eV, EDFE is determined by the second-derivative method, and in the range from 23 to 69 eV by derivation from the helium spectral-line intensities. Note that the nonmonotonic behavior of the distribution function due to inelastic collisions of electrons with gas atoms is clearly reflected both in the probe characteristics and in the radiation spectrum.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 71–76,. May, 1979.     

Relativistic effects on LEED intensities from Au(111)

Comparison of relativistically and nonrelativistically calculated intensity versus energy profiles in low energy electron diffraction (LEED) from the (111) surface of Au (Z = 79) reveals that relativistic corrections are quite significant. They can however, be obtained in very good approximation by quasirelativistic calculations, in which spin-averaged relativistic phase shifts are used as input for the nonrelativistic multiple scattering formalism. Further, relativistic effects on intensities are found to be comparable to differences arising from different approximations to the exchange part of the ion core potential.