Orbital Correspondence Analysis in Maximum Symmetry

A method is described in which the ‘allowed’ course of a reaction is determined by means of an analysis – within the symmetry point group common to reactants and products – of their molecular orbitals and of the distortions that occur along the reaction path connecting them. The procedure, and its relation to and advantages over conventional correlation methods, is illustrated with a few very well known reactions: Cyclization of hexatriene, the ‘photochemical Diels-Alder reaction’ and the stepwise and concerted [2+2]-cycloadditions.     

Tuning and switching of the spontaneous emission in one-dimensional photonic crystals

If the modal density available to an excited atom is varied on the time scale of its lifetime, then we can expect the natural process of spontaneous emission (SE) to become dynamically manipulable. We consider various experimental possibilities and focus on an atom embedded in a photonic crystal designed to have a band edge in the vicinity of the frequency of the emitted light. Specifically, we calculate the rate of SE by erbium ions (radiating at the wavelength 1.54 μm) implanted in a one-dimensional silicon/silica photonic crystal. The semiconductor layers are assumed to be strongly doped; by tuning the impurity density the free carrier concentration changes and the photonic bands shift. As a result, the SE rate exhibits significant dependency on the level of charge injection.