Optical absorption spectra and monomer interaction in polymers: Investigation of exciton coupling in DNA hairpins.

We investigate the effect of exciton coupling on the optical absorption spectra of polymer molecules under conditions of strong inhomogeneous broadening. It is shown that the dependence of the maximum in the rescaled absorption spectrum on the number of monomers is determined by their resonant exciton coupling and is insensitive to inhomogeneous broadening. Thus the absorption spectrum can be used to determine optical interactions between monomers. Using our theory and semiempirical calculations we determine exciton coupling between adjacent AT pairs in DNA to be 0.04 eV and discuss exciton localization in DNA hairpins composed of AT pairs.

Strong localization of positive charge in DNA induced by its interaction with environment.

We investigate a quantum state of positive charge in DNA. A quantum state of electron hole is determined by the competition of the pi-stacking interaction b sharing a charge between different base pairs and the interaction lambda with the local environment which attempts to trap charge. To determine which interaction dominates, we investigate charge quantum states in various (GC)(n) sequences choosing DNA parameters that satisfy experimental data for the balance of charge transfer rates G(+) <--> G(n)(+), n = 2, 3. We show that experimental data can be consistent with theory only assuming b< G(n)(+), n > or = 4 and comparing the experimental results with our predictions.

Charge-exchange-induced two-electron satellite transitions from autoionizing levels in dense plasmas.

Order-of-magnitude anomalously high intensities for two-electron (dielectronic) satellite transitions, originating from the He-like 2s(2) 1S0 and Li-like 1s2s(2) (2)S(1/2) autoionizing states of silicon, have been observed in dense laser-produced plasmas at different laboratories. Spatially resolved, high-resolution spectra and plasma images show that these effects are correlated with an intense emission of the He-like 1s3p 1P-1s(2) 1S lines, as well as the K(alpha) lines. A time-dependent, collisional-radiative model, allowing for non-Maxwellian electron-energy distributions, has been developed for the determination of the relevant nonequilibrium level populations of the silicon ions, and a detailed analysis of the experimental data has been carried out. Taking into account electron density and temperature variations, plasma optical-depth effects, and hot-electron distributions, the spectral simulations are found to be not in agreement with the observations. We propose that highly stripped target ions (e.g., bare nuclei or H-like 1s ground-state ions) are transported into the dense, cold plasma (predominantly consisting of L- and M-shell ions) near the target surface and undergo single- and double-electron charge-transfer processes. The spectral simulations indicate that, in dense and optically thick plasmas, these charge-transfer processes may lead to an enhancement of the intensities of the two-electron transitions by up to a factor of 10 relative to those of the other emission lines, in agreement with the spectral observations.