Development of several new computational approaches within the framework of multi-reference ab initio
 molecular electronic structure methodology and their implementation in the COLUMBUS program system are reported.
 These new features are: calculation of the analytical MR-CI gradient for excited states based
 on state-averaged MCSCF orbitals, the extension of the MR-ACPF/AQCC methods to excited states in the framework
 of linear-response theory, spin–orbit CI for molecules containing heavy atoms and the development of
 a massively-parallel code for the computation of the one- and two-particle
 density
 matrix elements. Illustrative examples are given for each of these cases.

https://univie.ac.at/columbus/workshops/rio2005/lectures/szalay/papers/columbus2.pdf

High-level multireference methods in the quantum-chemistry program system COLUMBUS: Analytic MR-CISD and MR-AQCC gradients and MR-AQCC-LRT for excited states, GUGA spin–orbit CI and parallel CI density

A detailed study, using a panel of spectroscopic analytical methods, of the complexation between 1-hydroxyethane-1,1‘-diphosphonic acid (HEDP) and uranyl ion (UO22+) is reported. Results suggest that the metal complex is present as only 1:1 (metal/ligand) species at low concentration (<10-4 M). The conditional constants of this complex were determined at various pH using time-resolved laser-induced fluorescence (TRLIF) and electrospray ionization mass spectrometry (ESI-MS). Further investigations indicate the presence of a 1:2 (metal/ligand) complex at higher concentrations (∼10-2 M). Selectivity studies as well as structural aspects are presented.

Investigation of the interaction between 1-hydroxyethane-1,1'-diphosphonic acid (HEDP) and uranium(VI).

Results of an inter-laboratory round-robin study of the application of time-resolved emission spectroscopy (TRES) to the speciation of uranium(VI) in aqueous media are presented. The round-robin study involved 13 independent laboratories, using various instrumentation and data analysis methods. Samples were prepared based on appropriate speciation diagrams and, in general, were found to be chemically stable for at least six months. Four different types of aqueous uranyl solutions were studied: (1) acidic medium where UO22+aq is the single emitting species, (2) uranyl in the presence of fluoride ions, (3) uranyl in the presence of sulfate ions, and (4) uranyl in aqueous solutions at different pH, promoting the formation of hydrolyzed species. Results between the laboratories are compared in terms of the number of decay components, luminescence lifetimes, and spectral band positions. The successes and limitations of TRES in uranyl analysis and speciation in aqueous solutions are discussed.

/pdf/aqueous-solutions-of-uranium-vi-as-studied-by-time-resolved-ok0llhnc8w.pdf

Aqueous solutions of uranium(VI) as studied by time-resolved emission spectroscopy: A round-robin test

Spectroscopic characterization of uranium in evaporation basin sediments

Uranyl fluoride (UO2F2) is a compound which forms in the reaction between water and uranium hexafluoride, a uranium containing gas widely used for uranium enrichment. Uranyl fluoride exhibits negligible natural background in atmosphere; as a result, its observation implies the presence and active operation of nearby enrichment facilities and could be used as a tracer for treaty verification technologies. Additionally, detection of UO2F2 has a potential application in guiding remediation efforts around enrichment facilities. Laser-induced fluorescence (LIF) has been proposed in the past as a viable technique for the detection and tracking of UO2F2. We demonstrate that ultrafast laser filamentation coupled with LIF extends the capabilities of standard LIF to enable remote detection of UO2F2. An intense femtosecond laser pulse propagated in air collapses into a plasma channel, referred to as a laser filament, allowing for the extended delivery of laser energy. We first investigate the luminescence of UO2F2 excited by the second harmonic of an ultrafast Ti:sapphire laser and subsequently excite it using the conical emission that accompanies ultrafast laser filamentation in air. We measure the decay rates spanning 4.3–5.6 × 104 s−1 and discuss the characteristics of the luminescence for both ultrafast- and filament-excitation. Larger decay rates than those observed using standard LIF are caused by a saturated component of prompt decay from annihilation of dense excited states upon excitation with an ultrafast source. The reproducibility of such decay rates for the given range of incident laser intensities 1.0–1.6 × 1011 W cm−2 is promising for the application of this technique in remote sensing.

/pdf/ultrafast-laser-filament-induced-fluorescence-spectroscopy-13awdon3z5.pdf

Clatyon W Williams

Papers

Uranyl fluoride luminescence in acidic aqueous solutions