Investigation using13C and15N CP MAS NMR of potential solid state tautomerism of some indolinones

A¹³C and¹⁵N CP MAS NMR study is reported for seven molecules and the results are compared with those previously obtained from solution NMR. The close agreement between the two sets of results show that the tautomeric equilibria found in solution and the solid state are the same for the compounds investigated. In all cases formA is found to be essentially the only one present. An X-ray diffraction study is presented for a molecule which is a model for formA.     

Radiotracers in fluorine chemistry. Part IX fluorination of chlorofluoroethanes by chromia catalysts treated with hydrogen fluoride or hydrogen [18F]-fluoride

Passage of dichlorotetrafluoroethane isomers or 1,1,2-trichloro- 1,2,2-trifluoroethane at temperatures ? 623 K over chromia catalysts, previously treated with hydrogen fluoride at 623 K, leads to the formation of fluorinated and chlorinated products. Incorporation of fluorine-18 radioactivity in the products is observed when hydrogen [¹⁸F]-fluoride is used in the catalyst pretreatment, indicating the involvement of a surface fluorine- containing species. The reactions observed are described in terms of series of F-for-Cl and Cl-for-F halogen exchange reactions occurring at the catalyst surface.     

Substituent effects on one-bond 15N?13C couplings in N,N-dimethylanilines and nitrobenzenes. Effect of steric inhibition of conjugation

The ¹J(¹⁵N¹³C) values for a series of ring-substituted N,N-dimethylaniline-¹⁵N derivatives and a series of nitrobenzene-¹⁵N derivatives were measured from the ¹³C spectra. In the nitrobenzenes, small changes in ¹J(¹⁵N¹³C) are attributed to the inductive effect of the substituents, since steric inhibition of conjugation has little effect on the magnitude of the coupling. In contrast, steric inhibition of nitrogen lone-pair delocalization in N,N-dimethylaniline derivatives markedly reduces the value of ¹J(¹⁵N¹³C). Theoretical calculations of ¹J(¹⁵N¹³C) values for the two series of compounds were made using standard INDO parameters and a ‘sum-over-states’ perturbation approach. Fair agreement between the calculated and experimental values is found.     

Reaction profiles for kinetic studies of inhomogeneous reactions within solid organic films

A technique is described whereby an assessment of the extent of reaction at any time and at any selected depth beneath the surface of a solid film is obtained from infrared spectrophotometric data. The resultant reaction profiles can be used to investigate the kinetics in planes normal to the surface. Group concentration–time curves can be constructed for planes at selected depths parallel to the surface and used to assess the kinetics in such planes. As a result it is possible to study realistically reactions which do not occur homogeneously throughout a solid, e.g., those effected by oxidation, irradiation, plasma treatment, etc.     

Electron stimulated desorption of Xe,Kr, and Ar

Electron stimulated desorption cross sections have been measured for Xe, Kr, and Ar overlayers on the Ag(111) surface. The Xe cross section is less than 10^?4 Ų; the Kr cross section is strongly temperature dependent, rising from 0.1 Ų at 10 K to 0.18 Ų at 50 K; the Ar cross section is 4 Ų and temperature independent. These results are rationalized using a model of the stimulated desorption similar to that proposed by Antoniewicz [Phys. Rev. B21 (1980) 3811], in which an atom is ionized by the incident beam, accelerates towards its image and is neutralized, desorbing only if the kinetic energy gained is greater than the neutral atom binding energy at the neutralization position. Fitting these data requires an exceedingly rapid dependence of the neutralization on distance for these slow ions. Rather than the effect of the mass on the ion velocity, the most important effect in determining the diverse behavior of the different gases is that the equilibrium position for the heavier gases is farther up the overlap repulsive potential and so in a region of more rapid neutralization. The model identifies several contributions to the isotope effect, predicting it to be temperature dependent. The results are extremely sensitive to the anharmonicity of the holding potential.     

Spin glass behavior and non-ergodicity in amorphous iron-boron alloys

We report FMR measurements on amorphous Fe_xB_1-x thin films with x=0.47, 0.49 and 0.53. At low T we observe anomalies characteristic of the FM-SG transition. In addition, in the 0.47 and 0.49 alloys the resonance field, below ～80K, depends upon the rate of cooling. We suggest that this behavior is symptomatic of non-ergodicity in the spin glass state.     

Double diffraction dissociation and test of pomeron factorization at the CERN ISR

We report the observation of double diffraction dissociation in the process p + p → (pπ⁺π^?) + X at √s of 45 GeV and momentum transfer in the ?t range 0.15?0.53 GeV² at the CERN ISR. The relative rates for elastic, single and double dissociation reactions measured here are found to agree with the prediction of Pomeron factorization.     

Appearance potential spectroscopy of layer materials

It has been shown that soft X-ray appearance potential spectroscopy (SXAPS) can be used as a probe of the conduction band density of states in several of the layer transition metal dichalcogenides, where the pronounced structure seen for TiS₂ agrees well with X-ray absorption data. In contrast, the complex structure seen in the SXAPS of pyrolytic graphite has previously been interpreted in terms of strong plasmon coupling. However, we find that the SXAP spectrum for vacuum cleaved pyrolytic graphite shows details not readily explicable by such an argument but which agree well with what would be expected on the basis of a conduction band self-convolution model. Further strong support for this interpretation is derived from XPS and SXAPS studies of the isostructural, isoelectronic boron nitride.