Reggeon phases and the dual bootstrap program

Analyticity requirements lead to complex Regge vertices in multiparticle production amplitudes. Their effect is discussed within a dual, unitary and exchange-degenerate multi-Regge model. A resulting complex Regge vertex is incorporated in fixed-t model calculations of the reggeon bootstrap and the topological pomeron. The bootstrap condition for particle-particle scattering is unaffected but new j-plane singularities appear in Regge-Regge scattering amplitudes. The pomeron and reggeon intercepts determine the two parameters of our Regge vertex and admit two possible solutions: one is close to the naive phase rule (real vertex) and the other is complex and leads to a high lying non-leading pole in the pomeron channel.     

Classical limit of the Casimir entropy for scalar massless field

We study the Casimir effect at finite temperature for a massless scalar field in the parallel plates geometry in N spatial dimensions, under various combinations of Dirichlet and Neumann boundary conditions on the plates. We show that in all these cases the entropy, in the limit where energy equipartitioning applies, is a geometrical factor whose sign determines the sign of the Casimir force.     

Transition from Charge‐Transfer to Largely Locally Excited Exciplexes,from Structureless to Vibrationally Structured Emissions

Exciplexes of 9,10‐dicyanoanthracene (DCA) with alkylbenzene donors in cyclohexane show structureless emission spectra, typical of exciplexes with predominantly charge‐transfer (CT) character, when the donor has a relatively low oxidation potential (E_ox), e.g. hexamethylbenzene (HMB). With increasing E_ox and stronger mixing with a locally excited (LE) state, vibrational structure begins to appear with 1,2,3,5‐tetramethylbenzene and becomes prominent with p‐xylene (p‐Xy). A simple theoretical model reproduces the spectra and the radiative rate constants, and it reveals several surprises: Even in this nonpolar solvent, the fractional CT character of a highly mixed exciplex varies widely in response to fluctuations in the microscopic environment. Environments that favor the LE (or CT) state contribute more to the blue (or red) side of the overall spectrum. It is known that sparsely substituted benzene radical cations, e.g., p‐Xy^?+, are stabilized more in acetonitrile than the heavily substituted HMB^?+. Remarkably, ion pairing with DCA^?– in cyclohexane leads to even larger differences in the stabilization of these radical cations. The spectra of the low‐E_ox donors are almost identical except for displacements that approximately equal the differences in E_ox, even though the exciplexes have varying degrees of CT character. These similarities result from compensation among several nonobvious, but quantified factors.     

A comprehensive approach to method validation based on object technology

 Method validation procedure requires a strategy for collecting those validation data that are best adapted to the analytical technique used. A flexible and general approach based on Object Linking and Embedding technology is proposed. It allows a traceable validation strategy using modular objects which encapsulate documentation, analytical data and processing logic. The contents of these objects are accessible through a standard user interface. This paper demonstrates how this can reduce experiment time, simplify evaluation efforts, and increase the ease of use of validation figures of merit. An illustration using Microsoft Visual Basic for Applications is presented, and some specific aspects are described. It consists of the evaluation of a time domain NMR technique for determining the moisture content of foods involving a multivariate calibration step. This study also illustrates how guidelines such as Good Validation Practices could be defined to present all validation documents in a standardised manner. Received: 3 September 1996 Accepted: 14 October 1996     

Cationic polymerization with boron halides. III. BCl3 coinitiator for olefin polymerization

The polymerization of isobutylene with BF₃, BCl₃, and BBr₃ coinitiators has been investigated. The polymerization with BCl₃ requires the presence of a cationogen, e.g., H₂O. The presence of a polar solvent is also necessary. Surprisingly, large quantities of polar solvent are required for effective polymerization. To obtain high conversions, the mixing sequence of the reagents is critical: BCI₃ must be added last to charges containing the monomer and H₂O in a polar solvent. Ultimate conversions increase by decreasing the temperature. Kinetic termination exists. Experiments with BF₃ and BBr₃ revealed that polymerizations induced with BF₃ proceed in nonpolar and/or polar media. Polymerization stops with BF₃ at less than complete conversion (termination exists). In contrast to findings with BCl₃, polymer yields with BF₃ increase with increasing temperatures. BBr₃ is a very inefficient coinitiator, even in the presence of polar solvent, over the ?10 to ?90°C temperature range. A hypothesis which explains these observations has been developed.     

Models for the theory of the hydrogen bond: Linear H3/−

An analogy is drawn between the hydrogen bond and the interaction of H₂ with H^– as a prototype. The energy surface for linear H^3/– is calculated using a minimal basis set of 1s orbitals and complete configuration interaction. The appearance of single and double minimum potentials on this surface is discussed.Contribution No. 359 from the Department of Chemistry, Tufts University.