Search results for "Ground"
showing 10 items of 2432 documents
Advances in Mössbauer Emission Spectroscopy
1990
After effects following nuclear transformation have been extensively studied in a large variety of matrices by Mossbauer Emission Spectroscopy (MES). The branching ratios of transient atomic charge states and energetically unstable states of the environment, excitations of electronic ligand field states and populations out of equilibrium within the electronic ground state manifold have been studied. Recent developments and also new insights and understandings of different aspects of the aftereffects of radioactive decay of57Co in semiconductors and molecular crystals are reviewed. A detailed picture of the decay process within the electronic states of the nucleogenic Fe3+ species could be o…
Metastable electronic states induced by nuclear decay and light
1994
Radioactive atoms incorporated in insulating solid-state compounds create various kinds of chemical and physical “after-effects” upon nuclear disintegration. Mossbauer emission spectroscopy of57Co-labelled coordination compounds has undoubtedly become the most informative technique to detect such after-effects like aliovalent charge and spin states of the nucleogenic iron atom resulting from the57Co(EC)57Fe decay, low energy excitations of crystal field and Zeeman states, linkage isomerism, radical formation with subsequent redox reactions, and others. We have extensively studied57Co-labelled complexes with [CoIIN6] cores employing time-integral and time-resolved Mossbauer emission spectros…
A Heteroleptic Push-Pull Substituted Iron(II) Bis(tridentate) Complex with Low-Energy Charge-Transfer States
2014
A heteroleptic iron(II) complex [Fe(dcpp)(ddpd)](2+) with a strongly electron-withdrawing ligand (dcpp, 2,6-bis(2-carboxypyridyl)pyridine) and a strongly electron-donating tridentate tripyridine ligand (ddpd, N,N'-dimethyl-N,N'-dipyridine-2-yl-pyridine-2,6-diamine) is reported. Both ligands form six-membered chelate rings with the iron center, inducing a strong ligand field. This results in a high-energy, high-spin state ((5) T2 , (t2g )(4) (eg *)(2) ) and a low-spin ground state ((1) A1 , (t2g )(6) (eg *)(0) ). The intermediate triplet spin state ((3) T1 , (t2g )(5) (eg *)(1) ) is suggested to be between these states on the basis of the rapid dynamics after photoexcitation. The low-energy …
Multi-frequency EPR studies of a mononuclear holmium single-molecule magnet based on the polyoxometalate [Ho(III)(W5O18)2]9-.
2012
Continuous-wave, multi-frequency electron paramagnetic resonance (EPR) studies are reported for a series of single-crystal and powder samples containing different dilutions of a recently discovered mononuclear Ho(III) (4f(10)) single-molecule magnet (SMM) encapsulated in a highly symmetric polyoxometalate (POM) cage. The encapsulation offers the potential for applications in molecular spintronics devices, as it preserves the intrinsic properties of the nanomagnet outside of the crystal. A significant magnetic anisotropy arises due to a splitting of the Hund's coupled total angular momentum (J = L + S = 8) ground state in the POM ligand field. Thus, high-frequency (50.4 GHz) EPR studies reve…
ChemInform Abstract: Excited State Decay of Cyclometalated Polypyridine Ruthenium Complexes: Insight from Theory and Experiment
2016
Deactivation pathways of the triplet metal-to-ligand charge transfer (3MLCT) excited state of cyclometalated polypyridine ruthenium complexes with [RuN5C]+ coordination are discussed on the basis of the available experimental data and a series of density functional theory calculations. Three different complex classes are considered, namely with [Ru(N^N)2(N^C)]+, [Ru(N^N^N)(N^C^N)]+ and [Ru(N^N^N)(N^N^C)]+ coordination modes. Excited state deactivation in these complex types proceeds via five distinct decay channels. Vibronic coupling of the 3MLCT state to high-energy oscillators of the singlet ground state (1GS) allows tunneling to the ground state followed by vibrational relaxation (path A…
Ferromagnetism in Cu II 4 and Co II 4 Complexes Derived from Metal‐Assisted Solvolysis of Di‐2,6‐(2‐pyridylcarbonyl)pyridine: Syntheses, Structures, …
2008
Metal-assisted solvolysis of di-2,6-(2-pyridylcarbonyl)pyr-idine (pyCOpyCOpy, dpcp) by M(0 2 CMe) 2 ·xH 2 O (M II = Cu II , CO II ) led to complex [Cu 4 {pyC(O) 3 pyC(O)(OEt )py}(O 2 CMe )5-(EtOH) 2 ] (1), when the reaction was carried out in EtOH, and to complex [Co4{pyC(O)(OMe )pyC(O)(OMe )py} 2 (02CMe)2-(N 3 ) 2 ] (2), when the reaction was carried out in MeOH in the presence of azide anions. Complex 1 consists of four Cu II ions bridged by the hemiacetal-gem-diol form of the ligand, which is found in a μ 4 -η 2 :η 2 :η 2 :η 1 :η 1 :η 1 coordination mode. It exhibits ferromagnetic couplings among all nearest neighbors and antiferromagnetic next-nearest-neighbor interactions (J 12 = J 1 =…
Light Dark Matter Search with Ionization Signals in XENON1T
2019
We report constraints on light dark matter (DM) models using ionization signals in the XENON1T experiment. We mitigate backgrounds with strong event selections, rather than requiring a scintillation signal, leaving an effective exposure of (22±3) tonne day. Above ∼0.4 keVee, we observe <1 event/(tonne day keVee), which is more than 1000 times lower than in similar searches with other detectors. Despite observing a higher rate at lower energies, no DM or CEvNS detection may be claimed because we cannot model all of our backgrounds. We thus exclude new regions in the parameter spaces for DM-nucleus scattering for DM masses mχ within 3–6 GeV/c2, DM-electron scattering for mχ>30 MeV/c2, a…
Combined Theoretical and Experimental Study of the Photophysics of Asulam
2013
The photophysics of the neutral molecular form of the herbicide asulam has been described in a joint experimental and theoretical, at the CASPT2 level, study. The unique π → π* aromatic electronic transition (f, ca. 0.5) shows a weak red-shift as the polarity of the solvent is increased, whereas the fluorescence band undergoes larger red-shifts. Solvatochromic data point to higher dipole moment in the excited state than in the ground state (μ(g)μ(e)). The observed increase in pKa in the excited state (pKa* - pKa, ca. 3) is consistent with the results of the Kamlet-Abboud-Taft and Catalán et al. multiparametric approaches. Fluorescence quantum yield varies with the solvent, higher in water (…
New circuital models of grounding systems and PDS for EMI analysis during a lightning strike
2005
In this paper circuital models of a Power Drive System (PDS) and of grounding systems are proposed in order to analyse Electromagnetic Interferences (EMI) induced in a PDS when a lightning current flows in the grounding system. The models have been developed adopting the network approach with lumped parameters and have been implemented using the software MATLAB. A High Frequency (HF) model suitable to simulate the impulse response of a PDS is described and a generalized method in order to calculate the lumped parameters values of grounding system models is presented. The new method takes into account the burial depth of electrodes as regards their length. The validation results of this new …
Student-initiated multi-unit questions in EMI classrooms
2021
This conversation analytic study investigates student-initiated multi-unit questions (MUQs) in whole class interaction. Based on a corpus of 30 hours of videotaped interactions from teacher education classrooms in an English-medium instruction university, we demonstrate that students use MUQs to introduce topics, either by recontextualizing some aspect of the prior topic, or alternatively, without these cohesive ties, which requires more interactional work to achieve intersubjectivity. Findings reveal that MUQs render student professional concerns more relevant and salient, foregrounding those inquiries as a space for launching topics. Students bring up issues such as ways of handling parti…