The effect of solar radiation on the dissolved absorption coefficient (a CDOM []), which reflects the concentration of chromophoric dissolved organic matter (CDOM), was investigated in several lakes near Bariloche, Argentina and in northeastern Pennsylvania, USA. Samples of 0.2 m filtered lake water were exposed in quartz tubes to different portions of the solar spectrum using optical cutoff filters to remove parts of the ultraviolet (UV) region of the solar spectrum. Changes in the spectral absorption in these samples and the absorbed incident energy were used to calculate spectral weighting functions (SWFs) for the photobleaching (PB) of CDOM. PB was measured as the loss of a CDOM () (the a CDOM [] was averaged from 280 to 500 nm) per unit absorbed energy. CDOM from humic and clear lakes, as well as from a Sphagnum bog and an algal culture, was used in the experiments covering a wide range of carbon sources. We used an iterative, nonlinear optimization method to fit the measured results to a simple exponential function in order to generate each SWF. Comparing individual SWFs calculated for various CDOM sources, we computed a summary SWF from the experiments using epilimnial CDOM from our study lakes. Our summary SWF was able to explain 80-90% of the observed variance in our exposure experiments, and we were able to predict PB results obtained for other Argentine lakes (mean error 14.5%). Finally, we calculated that the effect of UV-B radiation on PB was small (Ͻ20% of total decrease in the absorption coefficient) compared to UV-A and blue light radiation. This suggested that increased UV-B radiation due to stratospheric ozone depletion would not greatly increase the photobleaching of whole water column CDOM in Patagonian lakes (Ͻ10%).

We report fully differential cross-section calculations using distorted wave theories for helium single ionization by 75 keV p impact. Comparisons are made with absolute experimental data and we find that good results are obtained in the magnitude without the need for normalization factors. However, discrepancies are quite apparent in the position and shape of the peak structures in the fully differential angular distribution of the ejected electrons. We assess the influence of the internuclear interaction on low-energy electron emission in the scattering plane and in the perpendicular plane. Our continuum distorted wave-eikonal initial state calculations with (without) the internuclear interaction yield better results for the large (small) momentum transfer. We discuss this behaviour as a consequence of active electron screening for lowenergy electron emission.

Abstract.In this work we present fully differential cross sections (FDCSs) calculations using post and prior version of CDW-EIS theory for helium single ionization by 100 MeV C 6+ amu −1 and 3.6 MeV amu −1 Au 24+ and Au 53+ ions. We performed our calculations for different momentum transfer and ejected electron energies. The influence of internuclear potential on the ejected electron spectra is taken into account in all cases. We compare our calculations with absolute experimental measurements. It is shown that prior version calculations give better agreement with experiments in almost all studied cases.

In this work, we present fully differential cross section (FDCS) calculations using distorted wave theories for helium single ionization by 2 MeV amu−1 C6+ ions. We study the influence of internuclear interaction on low-energy electron emission in the scattering plane. It is shown that by incorporating an internuclear effective charge which depends on the collision momentum transfer and taking into account its interplay with passive electron screening we obtain better agreement with experiments in most cases under consideration. Comparisons are made with absolute experimental measurements and with other theories. We found that for ejected-electron momentum similar to transferred momentum, internuclear potential effects have little contribution to FDCSs.