Direct detection of the biradicals generated in the Norrish type II reaction

The biradicals generated in the Norrish type II reaction from the triplet manifold have been observed using laser flash photolysis techniques. The spectra and extinction coefficients closely resemble those of typical ketyl radicals. Typical lifetimes are in the 40–100 ns range depending on the solvent. Their interaction with oxygen is essentially diffusion controlled.     

Isotope dynamic mixing and vibronic structure

Existing theories which deal with the isotope dependence of vibronic structure have neglected the isotope dependence of vibration dynamics. The latter dependence (isotope dynamic mixing) is an adiabatic correction to vibronic structure theory. A theory of vibronic structure, which includes isotope dynamic mixing, is developed. The results of model calculations are presented.     

Application of parallel processing techniques to improving the efficiency of MM2 molecular mechanics calculations

The application of parallel processing techniques to molecular mechanics calculations is evaluated. Using the standard molecular mechanics package, MM2, four different parallel versions of the program are implemented in a four-processor computing environment. A set of 529 test structures is used to compare the efficiency of the parallel versions of MM2 to a standard serial version of the program. Statistics describing execution times and program execution cycles are gathered and analyzed. The effects of parallel processing overhead and computer system load are explored, and the practical utility of parallel processing in molecular mechanics is estimated. The results of these parallelization experiments indicate that for geometry optimizations requiring significant amounts of computing time an improvement in program execution speed approaching 50% is realizable. © 1993 John Wiley & Sons, Inc.     

The temperature dependence of coherent two-photon processes in naphthalene in the strong exciton-photon coupling regime

Temperature-dependent intensity data for two-photon excitation and second harmonic generation signals phase matched onto the polariton branches of the single a-exciton of naphthalene are presented. The data are shown be in quantitative agreement with the polariton fusion model which accounts for strong exciton-photon coupling. In this model the polariton scattering frequency and group velocity determine the branching ratios for the above signals.     

A comparison of the electrode kinetics of dissolution of Pb and Hg

Mercury dissolution in HCl and Pb in H₂SO₄ have been investigated using automated equipment of new design. The characteristic electrochemical parameter curves derived from the steady-state impedance and current-potential curves are reported. The data spans the active-passive transition and the passive region. An interpretation of the data in the passive region, based on a reaction kinetic model, is discussed.     

An additivity principle for Goldie rank

LetA be a noetherian ring. In generalA will not admit a classical Artinian ring of quotients. Yet a problem in enveloping algebras leads one to consider the possible embedding ofA in a prime ringB which is finitely generated as a left and a rightA module. Under certain additional technical assumptions, it is shown that the setS of regular elements ofA is regular inB and is an Ore set in bothA andB withS ⁻¹ A andS ⁻¹ B Artinian. This enables one to establish the following additivity principle for Goldie rank. Let {P ₁,P ₂, …P ₁} be the set of minimal primes ofA. Then under the above conditions it is shown that there exist positive integersz ₁,z ₂, …,z, such that , where rk denotes Goldie rank. This applies to the study of primitive ideals in the enveloping algebra of a complex semisimple Lie algebra. This paper was written while the authors were guests of the Institute for Advanced Studies, The Hebrew University of Jerusalem. The first author was on leave of absence from the Centre Nationale de la Recherche Scientifique, France.     

Spectral and scattering theory for a Schrödinger operator with a class of momentum-dependent long-range potentials

Let be the selfadjoint operator for the static electromagnetic field where W _j for 0, 1, 2, ..., n is a sum of (i) a short-range potential and (ii) a smooth long-range potential decreasing at as |x|^- with in (0, 1]. Then for >1/2, asymptotic completeness holds for the scattering system (H, H ₀).