By in situ energy-dispersive X-ray absorption spectroscopy (EDXAS) and X-ray diffraction (XRD), we analyzed the evolution of niobium in a MgH2/Nb2O5 system based on high-energy ball milling during hydrogen cycling. The high time resolution of the EDXAS method allowed us to monitor fast sample changes during this process. Thereby, we demonstrated that the Nb2O5 is already partially reduced during the milling process with the MgH2. Further reduction occurs during the heating and cycling processes, in which a lower limit of oxidation state is reached. Hereby, a reaction between the niobium oxide and the Mg/MgH2 leads to a decrease of crystalline Nb2O5 and the formation of a ternary oxide phase Mg x Nb y O. During the cycling processes a repetitive Nb oxidation−reduction process was observed, which may indicate hydrogen diffusion along the ternary oxide by the formation of metastable niobium hydrides. This points to a mechanism of kinetic sorption improvement by diffusion of hydrogen through pathways of ternary Mg−Nb oxides, which may also reduce the activation energy of the Mg−MgH2 transition.

The ground-state rotational spectrum of the tetrahydrothiophene···water complex (C4H8S···H2O) has been studied by free jet millimeter wave absorption and molecular beam Fourier transform microwave spectroscopy. The spectra of H2O and D2O combined with C4H8 32S and C4H8 34S were assigned. The rotational parameters have been interpreted in terms of a geometry in which the water molecule acts as proton donor lying close to the plane bisector to the CSC angle of tetrahydrothiophene. The “free” hydrogen is entgegen to the ring. The parameters characterizing the hydrogen bond are the distance between the sulfur and hydrogen atoms, r(S···H) = 2.37(4) Å, and the angle between the line bisecting the CSC angle of tetrahydrothiophene and the S···H bond, φ = 85.(3)°. The deviation from collinearity of the atoms S···H−O is suggested from θ = 162.(12)°.