Unusual selectivities of radical reactions. Experimental studies on alkyl versus phenoxyl reaction systems

Radical reactions involving two or more intermediates and many mutual reaction channels may lead to the specific formation of one cross-reaction product if one species is rather persistent and if transient and persistent species are produced with equal rates. A previous kinetic analysis of the phenomenon revealed that the concentrations of the intermediates and the selectivities of product formation depend critically on the relative initiation rates. The present experimental ESR studies on systems involving simultaneously generated phenoxyl radicals as persistent and alkyl radicals as transient species confirm the predicted behavior. They also lead to absolute rate constants for reactions of alkyl with phenoxyl radicals and for hydrogen atom transfer from phenols to alkyl radicals.     

Allowed transitions and intercombination lines in B II

Systematic multiconfiguration results are reported for the 2s ^{2 1} S ₀ → 2s2p ³ P ₁ intercombination line in B II. Both Breit-Pauli and fully relativistic calculations have been performed. The two methods are compared and the results are found to be in good agreement. Length and velocity forms of the oscillator strengths of related allowed transitions are also reported. The latter are used as a check on accuracy along with term energy separation. Fine-structure splitting is also reported but shown not to be a check on accuracy in the Breit-Pauli approximation.     

Zur Bestimmung der Verbrennungsw?rme

Ohne Zusammenfassung     

Photorefractive saturable absorptive and dispersive optical bistability

It is shown that photorefractive wave-mixing gives saturable gain, saturable absorption and Kerr-like nonlinear phase retardation. An analogy between photorefractive two-beam coupling and two-level atom system is then drawn. We investigate optical bistability in a ring cavity, utilizing these phenomena, and compare our results with classical absorptive and dispersive optical bistability.