Photolysis of 1,1,1-difluorochloroethane (Freon 142) at 147 nm

1,1,1-Difluorochloroethane (Freon 142) was photolyzed at 147 nm in the pressure range of 3.6–20.6 torr. The effects of added NO, H₂S, and CF₄ were investigated. The extinction coefficient at 147 nm and 296°K was determined to be 64 ± 8 atm^?1 · cm^?1. The molecule photodecomposes largely by α,β elimination of HCl to give 1,1-difluoroethylene (Φ = 0.74 ± 0.06). There is no observable elimination of HF, but there is strong evidence for the elimination of the elements of FCl though the relative importance of this process is minor, as are contributions from carbon? carbon and carbon? halogen bond fission. The 1,1-difluoroethylene formed is undoubtedly vibratonally excited and is the source of a pressure-dependent small yield of fluoroacetylene. Over the pressure range studied there is no evidence that the major primary process itself is affected by changes in total pressure as is the case in the 147-nm photolysis of ethyl chloride.     

Dielectric relaxation in coexisting nematic and smectic B phases

Mixtures of a polar solute 4-n-pentyl-4'-cyanobiphenyl in a non-polar nematic solvent exhibit two separated low frequency dielectric relaxations for concentrations of the solute between 2 mol% and 20 mol% over a limited temperature range. This behaviour is attributed to coexisting nematic and smectic B phases, in which the polar solute probe has different relaxation frequencies. The observed dielectric spectra can be accurately fitted to two Debye-like relaxations, and the strengths of the absorptions are proportional to the amounts of the coexisting phases. A microscopic determination of the phase diagram confirms the assignment of the coexisting phases, and it is concluded that there is a preference of the dipolar probe molecule for the smectic B phase, which is induced as a result of solute-solvent interactions.     

Implications of the Glueball-qq¯ filter on the 1++ nonet

The application of our glueball-qq¯ filter to the centrally produced KK¯ system shows that the f ₁(1285) and f ₁(1420) have the same behaviour; namely consistent with the f ₁(1420) being the partner to the f ₁(1285) in the 3P1 nonet of axial mesons. We determine a flavour singletoctet mixing angle of ~ 50° for this nonet and highlight that the existence of the supposed f ₁(1510) needs confirmation.     

Principal Bundles and the Dixmier Douady Class

A systematic consideration of the problem of the reduction and “lifting” of the structure group of a principal bundle is made and a variety of techniques in each case are explored and related to one another. We apply these to the study of the Dixmier-Douady class in various contexts including string structures, bundles and other examples motivated by considerations from quantum field theory. Received: 26 February 1997 / Accepted: 5 August 1997     

Monopoles and spectral curves for arbitrary Lie groups

The definition of the spectral curve of a monopole is extended to any connected, compact, simple Lie groupK. It is found there are rankK curves whose degrees are related to the topological weights of the monopole.     

Multiplicity dependence of the pion source in S+A collisions at the CERN SPS

The emission of pions from relativistic heavy-ion collisions of S+S, S+Ag and S+Pb at 200 GeV/nucleon is characterized using two-particle interferometry. The multiplicity dependence of the pion source parameters near midrapidity is studied. The transversal (R _t) and longitudinal (R _l) pion source parameters are independent of the initial nuclei in the interaction and increase with increasing multiplicity. This suggests that the freeze-out process is governed mainly by the particle multiplicity. The multiplicity dependence is weaker than that expected from a simple model of a freeze-out at a constant density.