Double strand breaks in DNA resulting from double-electron-emission events

A mechanism of double strand breaking (DSB) in DNA due to the action of two electrons is considered. These are the electrons produced in the vicinity of DNA molecules due to ionization of water molecules with a consecutive emission of two electrons, making such a mechanism possible. This effect qualitatively solves a puzzle of large yields of DSBs following irradiation of DNA molecules. The transport of secondary electrons, including the additional electrons, is studied in relation to the assessment of radiation damage due to incident ions. This work is a stage in the inclusion of Auger mechanism and like effects into the multiscale approach to ion-beam cancer therapy.Comment: 4 pages, 3 figure

A vibrationally resolved experimental study of the sulfur L-shell photoelectron spectrum of the CS2 molecule

The sulfur L-shell photoelectron spectrum of the carbon disulfide molecule has been studied using monochromated synchrotron radiation with a photon energy of 250 eV. The spectrum is atomic like, showing three major bands that can be associated with the sulfur (2p-1)2P3/2,12 and (2s-1)2S1/2 ionic states. A closer inspection shows that the 2P3/2 state is further split into two components separated by 128 meV due to the molecular field. The resulting ionic states are located at 169.806 eV (0-0 energy), 169.934 eV (0-0 energy), 171.075 eV (0-0 energy) and 237.05 ± 0.2 eV (centroid), respectively. Vibrational progressions in the (2p-1) bands are attributed to the asymmetric v3 mode, which gives evidence of a localization of the core hole. The following values were obtained for the vibrational constants: ωe = 196.7 ± 1.1 meV; ωdxe = 0.2 ± 0.5 meV. A curve fit of the vibrational lines using a Voigt function gave a natural width of 59.6 ± 1.8 meV for the (2p-1) states, corresponding to a lifetime of 11 fs, and a spectrometer broadening of 38.2 ± 1.8 meV. The (2p-1) bands are accompanied by shake-up structures occurring at 6-18 eV higher energies. They are interpreted mainly in terms of excitations to the unoccupied 3πu* orbital in the final ionic state. The (2s-1)2S1/2 band is broad and structureless due to fast Coster-Kronig processes. A fitting of a Voigt function gives a natural line-width of 1.85 eV which corresponds to a lifetime of 0.4 fs

Time resolved experiment with a VUV pump pulse

227th ACS National Meeting, Anaheim, CA, MAR 28-APR 01, 2004International audienceno abstrac

Evidence of ultra-fast dissociation in ammonia observed by resonant Auger electron spectroscopy

We present evidence for ultra-fast dissociation of molecular ammonia when photo-excited to the Nls --> 4a(1) core-hole state. This finding is based on resonant Auger spectroscopical results as well as qualitative arguments concerning the photon energy dependence of the Auger structures. Calculations of the excited state potential based on the Z + l approximation were performed. Both the calculations and the measurements indicate that the most likely fragmentation pathway for the core excited ammonia molecules leads to NH2* and H fragments. (C) 2003 Elsevier Science B.V. All rights reserved

Constant-atomic-final-state filtering of dissociative states in the O1s->sigma* core excitation in O_2

The below-threshold region in core-excited O2 is very complex, consisting of a multitude of exchange-split states with mixed molecular orbital-Rydberg character. We have investigated the nature of these intermediate states by resonant Auger spectroscopy. In particular, we have obtained constant-atomic-final-state yield curves for several atomic peaks in the electron decay spectra which are stemming from ultrafast dissociation. The relative intensity of Auger decay leading to atomic final states is considered a signature of the relative weight of the sigma* character. This method allows one to "filter out" intermediate states with dissociative character. Extensive calculations have been performed by multireference configuration interaction at different interatomic distances in order to evaluate the potential curves of the core-excited states and propose a qualitative description of the dissociative molecular dynamics. The calculations show that the core-excited states have a relevant admixture of excitations to orbitals with Rydberg character and excitations to the sigma* orbital with different spin couplings. A diabatization of the adiabatic potential curves shows that the coupling between Rydberg and sigma* diabatic states is very different at the different crossing points and ultrafast dissociation occurs more easily on the lowest sigma* diabatic potential curve. As a consequence, the observation of atomic peaks only in the lower-energy region of the absorption curve is well justified

Predictors of deterioration of lung function in cystic fibrosis.

The severity of lung disease in cystic fibrosis (CF) may be related to the type of mutation in the cystic fibrosis transmembrane conductance regulator (CFTR) gene, and to environmental and immunological factors. Since pulmonary disease is the main determinant of morbidity and mortality in CF, it is important to identify factors that can explain and predict this variation. The aim of this longitudinal study of the whole Swedish CF population over age 7 years was to correlate genetic and clinical data with the rate of decline in pulmonary function. The statistical analysis was performed using the mixed model regression method, supplemented with calculation of relative risks for severe lung disease in age cohorts.The severity of pulmonary disease was to some extent predicted by CFTR genotype. Furthermore, the present investigation is the first long-term study showing a significantly more rapid deterioration of lung function in patients with concomitant diabetes mellitus. Besides diabetes mellitus, pancreatic insufficiency and chronic Pseudomonas colonization were found to be negative predictors of pulmonary function. In contrast to several other reports, we found no significant differences in lung function between genders. Patients with pancreatic sufficiency have no or only a slight decline of lung function with age once treatment is started, but an early diagnosis in this group is desirable

High-resolution excitation-energy-dependent study of the Auger decay of the O 1s - 1IIg core-excitated state in oxygen

9 pagesWe report new measurements of the decay of the core-excited O 1s–1πg 3Πu state in molecular oxygen under Auger resonant Raman conditions. The spectral features are interpreted with the aid of ab initio calculations using standard lifetime-vibrational interference, and in some cases, employing a model in which the bond-length dependence of the Auger transition rates is taken into account. By analyzing a series of Auger-decay spectra using different excitation energies, several instances of fixed kinetic energy are pointed out in the spectra; the nondispersive behavior arises from the decay between two potentials that are essentially parallel