Infrared-microwave double-resonance spectroscopy of the ClO2 radical: A textbook example

The capability of the ir-mw double-resonance technique to produce precise spectroscopic data has been thoroughly tested in a study of the ClO₂ free radical. Although the experiments are based on fixed-frequency gas lasers, the results of the work show that rotational and vibrational information can be obtained from practically all infrared absorption bands of ClO₂ within the operating frequency range of the lasers. A wide range of microwave frequencies was searched using approximately 120 individual laser lines; double-resonance signals were observed with about 25% of the lines used. The double-resonance data obtained were sufficient to determine rotational, distortion, fine, and hyperfine constants for the vibrational states (0, 0, 0), (1, 1, 0), and (0, 0, 1) of ³⁵ClO₂ and (1, 0, 0) and (0, 0, 1) for ³⁷ClO₂. The constants for the (0, 0, 0) state of ³⁵ClO₂ and ³⁷ClO₂ and for (0, 1, 0) of ³⁵ClO₂ were refined and those for the (0, 1, 0) state of ³⁷ClO₂ were determined with data obtained from double-resonance and conventional measurements. The rotational constants obtained allowed equilibrium structures for both³⁵ClO₂ and ³⁷ClO₂ to be calculated. The structural parameters obtained in each case are in excellent agreement: $\text{r}{}_{\mathrm{e}}\text{= 1.4700(1}\text{A}\text{?}\text{)}$, θ_e = 117° 23.3′(7). The centers of the bands ν₁ and ν₁ + ν₂ ? ν₂ of ³⁵ClO₂ were precisely determined and the data available were sufficient to check the reliability of the values obtained. The band origins were also determined for ν₃, ³⁵ClO₂ and ³⁷ClO₂, and with less precision for ν₁ for ³⁷ClO₂.     

An interpretation of structural sorting diagrams for AB type compounds using molecular orbital ideas

The factors governing the structure adopted by a particular AB compound are investigated by deriving two parameters reflecting aspects of the interaction between A and B, using simple molecular orbital ideas, which can be quantified by use of atomic parameters derived from pseudopotential theory. A plot of the values of these two parameters, for a large database of compounds, produces a remarkable topological clustering of AB compounds with the same structure. This structural sorting can also be effected for nonoctet AB compounds if the number of electrons is taken into account. These parameters are related to other indices, R_σ, R_π, previously used by Bloch, Zunger, Phillips et al. to construct structural sorting diagrams. Hence we find a justification for the success of such displays, and shed light on the reasons underpinning structural preference, in terms of the number of valence electrons, and the relative positions of the energy levels of the constituent atoms. There appear to be strong similarities between the electronic reasons behind atomic site preferences in molecules and this site preference or coordination number problem in solids.     

Partial-wave analysis of the reactions pp → ϱ0ϱ0, ωϱ0, ϱ0f,and ωf in the T(2200) region

The helicity formalism is used to derive expressions for the joint decay distributions for ?⁰?⁰, ω?⁰, ?⁰f and ωf states in terms of the joint density matrix elements. These expressions are used to extract the density matrix elements from the data of the Rutgers- Stevens-Albany collaboration in the T(2200) region. A partial-wave analysis is then performed in an attempt to determine the dominant partial-wave amplitudes. The results are discussed and comparisons are made to the extremely limited amount of data available at neighboring energies. Finally it is pointed out that the expressions derived for this analysis could be applied without modification to e^?e⁺ annihilations into these states.     

The epitaxy of gold on (110) tungsten studied by leed

Growth of gold condensed on the (110) plane of tungsten has been studied using LEED and AES. Three ordered surface structures were observed when condensation takes place at or above 700 K, and no detectable order is seen below this temperature. Structure 1 is developed as the coverage approaches one monolayer and has gold atoms held in the W(110) array with a resultant 2% reduction in gold atom diameter. The second gold layer adopts the Au(111) structure with $\text{Au}\text{[1}\text{2}\text{1]}$ rotated by 2.5° from $\text{W}\text{[1}\text{1}\text{0]}$ and the first gold layer may also be constrained to adopt this structure. Deposition of more gold produces three dimensional crystallites with Au(111)∥W(110) which are double-positioned with their 121 directions parallel to the 121 directions of tungsten. Addition of half a monolayer of oxygen before condensation, completely prevents formation of structures 1 and 2. Instead, at coverages of 3 or more monolayers, three dimensional crystallites develop with Au(111) ∥ W(110) and $\text{Au}\text{[1}\text{2}\text{1] ∥}\text{W}\text{[1}\text{1}\text{0]}$. This behaviour is compared with the reported behaviour of copper and silver on W(110).     

Adsorption of lead on low-index planes of tungsten

Using probe-hole field emission microscopy the effect of adsorbed lead on the work function of the 100 and 110 planes of tungsten hasbeen studied and compared with the findings of Bauer et al. who studied the same system using LEED/Auger techniques. The effect of lead on the average work function $\text{}\text{?}$gf and that of (211) is also reported. Sub-monolayer lead increases φ(211) and this is ascribed to formation of a lead-tungsten dipole, the lead being negatively charged, with dipole moment 0.035 × 10^?30 C-m and polarizability 2.0 ų. On (110) lead reduces φ and behaves as a dipole with positively charged lead of moment 0.15 × 10^?30 C-m and polarizability 2.5 ų. φ(100) is also observed to decrease at low coverages equilibrated at low temperatures. This contrasts with Bauer's findings but is considered to result from failure of the Fowler—Nordheim model. With increasing lead coverage on all planes φ(hkl) tends to a constant value φ_sat. By comparison with Bauer et al. we can identify φ_sat on (110) as a compressed monolayer of lead. Likewise φ_sat produced by low temperature (～450 K) spreading on (100) is also associated with a compressed (1 × 1) structure. The lower value of φ(100) produced at higher temperatures (～850 K) is identified with the microfacetted surface observed by Bauer et al. Lead is observed to be absent from (110) when mean adatom densities as high as 8 × 10¹⁴ atoms cm^?2 are thermally equilibrated, and this is shown to result from the relatively low binding energy of lead on (110). The general agreement between the present findings and those of Bauer lends confidence to the belief that both techniques can detect the same behaviour despite the very large (10¹⁰) difference in the size of the area examined.     

A nuclear magnetic resonance study of toluene-polyisobutylene solutions. 2. Vrentas-Duda theory

The self-diffusion coefficients of toluene in polyisobutylene have been analyzed using the Vrentas-Duda free volume diffusion model. The diffusion coefficients were determined at different temperatures and concentrations, using the pulsed field gradient nuclear magnetic resonance technique. The data were satisfactorily described by the model and the size of the polymer jumping unit was extracted. Comparisons were made with the Fujita free volume theory and the Fujita free volume parameters were extracted from the Vrentas-Duda free volume parameters. From the diffusion data that now available, it can be concluded that for most polymers the jumping unit is about 1.5 times the polymer monomer molecular weight. The activation energy of the toluene diffusion in polyisobutylene is compared with the activation energies of other penetrants in the same polymer. The diffusion data presented in this work show that the energy per mole required to overcome the attractive forces which constrain a diffusing species to its neighbors should be considered to be zero, in order to be able to extract the free volume parameters (from viscosity and diffusion data) with an acceptable uncertainty. ©1995 John Wiley & Sons, Inc.     

Monomode fiber modulators: Frequency and polarization state control

Two experimental fiber components are described that exploit the properties of highly birefringent monomode optical fiber. In the first the generation of a traveling ultrasonic flexure wave on the fiber produces a frequency shift on the input optical signal. In the second a variable axial tension modulates the differential phase retardance between the two guided polarization eigenmodes to produce an arbitrary output polarization state from a linear input state (or vice versa) without loss of optical power.