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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,351 records · Page 75
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Putting chromium on the map for N 2 reduction: production of hydrazine and ammonia. A study of cis -M(N 2 ) 2 (M = Cr, Mo, W) bis(diphosphine) complexes

The first complete structurally and spectroscopically characterized series of isostructural Group 6 N 2 complexes is reported in this paper. Protonolysis experiments on cis-[M(N 2 ) 2 (P Et N R P Et ) 2 ] (M = Cr, Mo, W; R = 2,6-difluorobenzyl) reveal that only Cr affords N 2 H 5 + and NH 4 + from the reduction of the N 2 ligands.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Controlling the magnetic and optical responses of a MoS 2 monolayer by lanthanide substitutional doping: a first-principles study

Here, the electronic, magnetic and optical properties of lanthanide substitutional doping (~2% concentration) on the MoS 2 monolayer have been investigated within the density functional theory formalism together with the Hubbard correction (DFT+U). The dopants investigated include Ce, Eu, Gd, Lu and Tm. The calculated dopant substitutional energies under both Mo-rich and S-rich conditions suggest that it is possible to experimentally realize the lanthanide doped MoS 2 monolayer systems. The Eu, Gd and Tm dopants induce strong magnetization in the host lattice. The electronic structure calculations reveal that the dopants have a p-type character and they exhibit a half-metallic behavior in the Gd and Eu doped systems. A dilute magnetic semiconducting behavior can also be realized in Gd, Eu and Tm doped systems by slightly tuning the Fermi level. All the dopants refine the optical responses of the host system with the onset of the optical absorption edge shifting to lower energies within the visible range (red shift phenomenon). We observe an optical anisotropy for two different directions of the electric field (E) polarizations, i.e. parallel, E∥, and perpendicular, E⊥, to the xy-plane. Lanthanide substitutional doping significantly influences the electron energy loss spectra (EELS), absorption spectra, and dielectric properties of the host MoS 2 monolayer. Furthermore, we notice that lanthanide substitutional doping could enhance the photocatalytic properties of the MoS 2 monolayer.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Symmetry breaking charge transfer as a means to study electron transfer with no driving force

Symmetry breaking charge transfer (SBCT) is a process where a symmetrically disposed pair of identical chromophores forms a charge transfer excited state with the hole and electron on different chromophores, i.e. chr–chr + hν → chr + –chr – . Herein we explore this process in two dipyrrin-based bichromophoric systems. One of these bisdipyrrins involved a pair of BODIPY chromophores linked by a single bond at their meso-positions (compound 1) and the other involved two dipyrrin ligands coordinated in a tetrahedral geometry at the Zn 2+ ion (compound 2). Both compounds show rapid SBCT in polar solvents and only dipyrrin based emission in nonpolar solvents, the latter arising from a dipyrrin localized excited sate (LE). By “tuning” the solvent polarity the equilibrium between the LE and SBCT states can be shifted to favor either state. Ultrafast transient absorption spectroscopy (TA) was used to probe the kinetics of the charge transfer for 2 in solvents where the electron transfer is endergonic, exergonic and has a ΔG close to zero. Our TA derived rates were used to predict fluorescence efficiencies in each of the different solvent systems and showed a good correspondence to measured values. Detailed density functional theory (DFT) and time dependent DFT were used to model the ground states as well as the LE and SBCT states of 1 and 2, in both polar and nonpolar media. Lastly, the ground and LE excited states show small dipole moments, while the SBCT states show dipole moments of 16.4 and 20.3 D for 1 and 2, respectively.

14 SOLAR ENERGY↗