J. C. Thomson

Halogen-promoted γ-alumina. I, The interactions of 36Cl- and 14C-labelled carbon tetrachloride and of 36Cl- and 2H-labelled hydrogen chloride with γ-alumina

Abstract The behaviour of [ 36 Cl]-chlorine and [ 14 C]-carbon labelled carbon tetrachloride at 500 K and of [ 36 Cl]-chlorine and [ 2 H]-hydrogen labelled anhydrous hydrogen chloride at 293 K towards calcined γ-alumina has been investigated under static conditions. Two types of surface chlorine species are formed using CCl 4 ; one type is inert with respect to [ 36 Cl]-chlorine exchange with anhydrous HCl at 293 K, the other is labile and behaves identically to the surface species resulting from treatment with HCl. Radiotracer and neutron activation analyses indicate that more chlorine is retained by samples treated with CCl 4 under the conditions used. The results of isotopic exchange reactions together with an examination of the CCl 4 reaction using IR spectroscopy and 27 Al MAS NMR spectra of chlorinated γ-alumina are used to make proposals about the nature of the acidic sites formed.

Radiotracers in fluorine chemistry: Part XVHalogen exchange and isomerization reactions involving chlorofluoroethanes on fluorinated chromia surfaces labelled with anhydrous hydrogen [18F]-fluoride, hydrogen [36Cl]-chloride or 1,1-di[36Cl]chlorotetrafluoroethane

Abstract Series of fluorination and chlorination reactions are observed when CCl2FCClF2 or C2Cl2F4 isomers are flowed at ca. 700 K over fluorinated chromia catalysts that have been labelled by prior treatment with H18F or H36Cl. These reactions result in the incorporation of the radiolabel in each component of the mixtures of C2Cl6-nFn that are formed. The probability of a radiolabel, [18F] or [36Cl], in a given component correlates directly with the degree to which that component has been fluorinated or chlorinated on the surface. The isomerization of CCl2FCClF2 to CCl3CF3 is an important reaction on fluorinated chromia at 700 K; [36Cl] tracer experiments indicate that the process is intramolecular. Isomerization of CClF2CClF2 probably occurs also but is less dominant in the overall behaviour observed.

Halogen-promoted γ-alumina Part II. The catalytic dehydrochlorination of 1,1,1-trichloroethane at room temperature on chlorinated γ-alumina

Abstract The dehydrochlorination of 1,1,1-trichloroethane vapour to give 1,1-dichloroethene and hydrogen chloride is catalysed by γ-alumina which has been chlorinated with carbon tetrachloride or carbonyl chloride at 500 K. Chlorination of γ-alumina with hydrogen chloride does not result in a catalyst for this reaction. 1,1-Dichloroethene reacts further to produce a purple, oligomeric material on the surface of chlorinated γ-alumina. The overall reaction of CH 3 CCl 3 has been followed using IR spectroscopy and [ 36 Cl]-chlorine as a radiotracer. The results obtained are consistent with dehydrochlorination occurring at strong Lewis acid surface sites, although the chlorine associated with these sites is not involved directly in the reaction.

Pion pair production in photon-photon interactions

The processγγπ+π− has been measured with complete particle identification. Cross-sections are presented from near threshold up to the region of thef(1270). In the mass range 0.5–0.7 GeV, crosssections are lower than the Born term predictions and show no evidence for an ε(600). The two-photon width of thef(1270) is found to be in agreement with previous results.

Ambient temperature catalytic fluorination of C1 to C3 chlorohydrocarbons and related compounds using oxide-supported organic layer catalysts

Abstract 1,1,1-Trichloroethane is fluorinated by HF at ambient temperature and pressure in the presence of organic layer catalysts, derived from CH 3 CCl 3 , C 3 Cl 4 or CH 3 CCl 2 CH 3 and supported on SF 4 -fluorinated γ-alumina or CCl 4 -chlorinated γ-alumina, to give CH 3 CCl 3− n F n . Related behaviour is observed when CH 3 CCl 2 CH 3 , CH 2 ClCCl 3 , CHCl 2 CHCl 2 and CHClCCl 2 are fluorinated using the supported organic layer catalyst derived from CH 3 CCl 3 . The product distributions observed suggest that the reactivity of the substrates can be correlated with their ability to undergo dehydrochlorination. The behaviour of CHCl 3 , CCl 4 , CCl 2 FCClF 2 and CCl 3 CF 3 under similar conditions is also reported.

Tests of the standard model with lepton pair production ine+e− reactions

The differential cross section of the reactione+e−→e+e− at a c.m. energy of 34.7 GeV has been measured. The result, together with our previously measurede+e−→α+α− data, are compared with the standard model predictions. We obtain for the weak neutral current couplings the valuesgv2=0.09×0.06,ga2=0.38×0.08. A fit of the Weinberg mixing angle gives the valuegv2=0.09×0.06,ga2=0.038×0.08. The data are also used to set limits on possible deviations from the pointlike structure of leptons. An upper limit for thee+e− coupling to a heavy spin 0 boson is also given.

Measurement and analysis of the reactionγγ→3π+3π-

We have measured the cross section of four charged pion production in photon-photon interactions in the invariant mass range 1.0≦Wγγ≦3.2 GeV and up toQ2=16 GeV2. For 1.2 GeV≦Wγγ≦1.7 GeV the process is dominated by ρ0ρ0 production with a rapid rise in cross section around 1.2 GeV, well below the nominal ρ0ρ0 threshold. The observed distributions in the two particle masses and in the production and decay angles are well described by an incoherent sum of the phase-space subprocesses γγ →ρ0ρ0, →ρ0π+π−, and →π+π−π+π−. A spin-parity analysis of the ρ0ρ0 system showsJP=2+ to dominate, although 0+ is also possible forWγγ≦1.4 GeV. Negative partity states are excluded.

Tensor meson excitation in the reaction γγ→K S 0 K S 0

AbstractIn the analysis of the reactione+e−→e+e−KS0Ks0 clear evidence for exclusive γγ→f2′ resonance production is observed. The productΓγγ ·B(f2′→K

Jet Production in Photon-Photon Interactions

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