Search

The infuence of relativistic effects, more specifically of spin–orbit coupling (SOC), on the geometric and energetic features of halogen bonds mediated through astatine (At) has been investigated through quantum chemistry calculations. For complexes between ammonia and diastatine or diiodine, the accounting of SOC results in stronger interaction energies with iodine, in contrast to scalar-relativistic calculations which predict astatine as a better halogen-bond (XB) donor. In AtI, where the competition is intramolecular, astatine always appears as the strongest XB donor. Whereas calculations in the absence of SOC predict that 15% of the XB complexes with toluene occur on the iodine atom, this population becomes three times lower when SOC is taken into account. The investigation of hypoastatous acid properties highlights a substantial decrease of the hydrogen-bond (HB) and XB interaction energies for AtOH when SOC is considered. The calculation of complementary electrostatic (electrostatic potential, VS,max) and charge transfer (local electrophilicity, ̉+S,max) descriptors provide guidelines for the rationalization of these trends, underlining the significant role of SOC in astatine electronegativity. Finally, the SOC effects are shown in AtI and AtOH to be significantly transferred from astatine to its neighbouring atoms, resulting in stronger alterations of their XB or HB properties than on the XB donating ability of astatine itself. [ABSTRACT FROM AUTHOR]

We report a series of measurements of the effect of an electric field on the frequency of the ultranarrow linewidth F 7 0 → D 5 0 optical transition of Eu 3 + ions in an Y 2 SiO 5 matrix at cryogenic temperatures. We provide linear Stark coefficients along two dielectric axes and for the two different substitution sites of the Eu 3 + ions, with an unprecedented accuracy and an upper limit for the quadratic Stark shift. The measurements, which indicate that the electric field sensitivity is a factor of seven larger for site 1 relative to site 2 for a particular direction of the electric field, are of direct interest in the context of both quantum information processing and laser frequency stabilization with rare-earth doped crystals, in which electric fields can be used to engineer experimental protocols by tuning transition frequencies. [ABSTRACT FROM AUTHOR]

We demonstrate a method for accurately locking the frequency of a continuous-wave laser to an optical frequency comb under conditions where the signal-to-noise ratio is low, too low to accommodate other methods. Our method is typically orders of magnitude more accurate than conventional wavemeters and can considerably extend the usable wavelength range of a given optical frequency comb. We illustrate our method by applying it to the frequency control of a dipole lattice trap for an optical lattice clock, a representative case where our method provides significantly better accuracy than other methods. [ABSTRACT FROM AUTHOR]

Abstract: Astatine is a rare radioelement belonging to the halogen group. Considering the trace amounts of astatine produced in cyclotrons, its chemistry cannot be evaluated by spectroscopic tools. Analytical tools, provided that they are coupled with a radioactive detection system, may be an alternative way to study its chemistry. In this research work, high performance anion exchange chromatography (HPAEC) coupled to a gamma detector (γ) was used to evaluate astatine species under reducing conditions. Also, to strengthen the reliability of the experiments, a quantitative analysis using a reactive transport model has been done. The results confirm the existence of one species bearing one negative charge in the pH range 2–7.5. With respect to the other halogens, its behavior indicates the existence of negative ion, astatide At−. The methodology was successfully applied to the speciation of the astatine in human serum. Under fixed experimental conditions (pH 7.4–7.5 and redox potential of 250mV) astatine exists mainly as astatide At− and does not interact with the major serum components. Also, the method might be useful for the in vitro stability assessment of 211At-labeled molecules potentially applicable in nuclear medicine. [Copyright &y& Elsevier]