Helmholtz-Zentrum Dresden-Rossendorf e. V.

In the present work, an improved GC/MS method for the analysis of the reaction products of the non-catalytic partial oxidation of isobutane at a starting temperature of 25°C has been developed and compared to a previously published method [1]. Two green GC-solvents (dimethyl carbonate (DMC), diethyl carbonate (DEC)) and several internal standards (hexane, benzene, toluene, DEC) have been tested. The separation of the products at low retention times (methanol, isobutane, isobutene) could be significantly improved. For the liquid main products t-butyl hydroperoxide (TBHP), di-t-butyl peroxide (DTBP), t-butanol (TBA), propanone and most trace products (isopropanol, isobutanal, methyl formate, isopropyl formate, t-butyl formate and some acetates - 24 compounds in total), a coefficient of determination CoD > 0.999 has been achieved. For all weighing and GC/MS measurements uncertainties have been calculated. The peaks of the peak pair t-butyl formate (CoD >0.999) and isobutanol (CoD >0.99), have been simulated and used for calibrations. DEC gave a decomposition of TBHP on the column. With DMC, a problem of peak purity of TBHP appeared but could be resolved. The use of the green solvent DMC, compared to also studied traditional solvents like heptane and toluene, proved to be very beneficial, since it also permitted to determine polar compounds, e. g. carbon dioxide and formic acid.

The potential of gluconate, a common cement additive, to mobilize lanthanides (used as analogues of actinides) from cement is investigated. For this purpose, complex formation of trivalent lanthanides, Ln(III), (Ln: La, Sm, Eu, Gd, Lu) with gluconate (GLU) was studied applying time-resolved laser-induced luminescence spectroscopy (TRLFS) in combination with parallel factor analysis (PARAFAC), capillary electrophoresis-inductively coupled plasma mass spectrometry (CE-ICP-MS), nuclear magnetic resonance (NMR) spectroscopy, and density functional (DF) calculations. Up to circumneutral conditions, binary complexes form with Ln(III):GLU stoichiometric ratios of 1:1-1:4 depending only on the Ln:GLU ratio, regardless of the concentration regime (micromolar to millimolar). Coordination facilitates via the carboxyl group (C1) and the adjacent hydroxyl group (at C2) forming a five-membered ring chelation motif, with a probable participation of the C3 hydroxyl group. Beyond circumneutral pH, with the exact onset depending on the specific lanthanide, a fundamental change in speciation takes place. Speciation then becomes more complex upon coexistence and interconversion of several (isomeric) complexes concluded to involve one or more deprotonated GLU hydroxyl groups not necessarily participating in coordination.

Suitably normalized differential probabilities of one-photon emission in external electromagnetic fields are compared to quantify the transit of nonlinear Compton scattering to linear Compton scattering, described by the Klein–Nishina formula, and to constant-crossed field treatment. The known Klein–Nishina suppression at large energies is further enforced by increasing field intensity. In view of the Ritus–Narozhny conjecture, we demonstrate that different paths in the field intensity versus energy plane toward large values of the quantum nonlinearity parameter $$\chi $$χ facilitate significantly different asymptotic dependencies, both in the Klein–Nishina regime and the constant-crossed field regime and in between.

Differential perspective on the Klein-Nishina effect in strong-field QED: showing the smooth transition from the constant-crossed field (CCF) through the infinite plane-wave approximation (IPA) to the linear Klein-Nishina limit, highlighting the asymptotic behavior of the differential cross sections.