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Navin Khaneja
The paper describes the design of broadband chirp excitation pulses. We first develop a three stage model for understanding chirp excitation in NMR. We then show how a chirp π pulse can be used to refocus the phase of the chirp excitation pulse. The resulting magnetization still has some phase dispersion in it. We show how a combination of two chirp π pulses instead of one can be used to eliminate this dispersion, leaving behind a small residual phase dispersion. The excitation pulse sequence presented here allows exciting arbitrary large bandwidths without increasing the peak rf-amplitude...
July 13, 2017: Journal of Magnetic Resonance
Anjali Maan, Ashish Tyagi, Vinod Prasad
A theoretical model of NAREX (non-adiabatic rotational excitation) and field-free molecular orientation by a short specific elliptically polarised laser pulses (EPLPs) driving a polar molecule is presented. By choosing the proper value of elliptically polarised field parameters, efficient field-free orientation could be achieved. It is demonstrated that NAREX can be controlled by various laser parameters, out of which pulse shape plays the most significant role. The effect of elliptic parameter on the rotational excitation and orientation dynamics is also under concern...
July 13, 2017: Spectrochimica Acta. Part A, Molecular and Biomolecular Spectroscopy
Jens Kügel, Markus Leisegang, Markus Böhme, Andreas Krönlein, Aimee Sixta, Matthias Bode
Molecular electronics where single molecules perform basic functionalities of digital circuits is a fascinating concept that one day may augment or even replace nowadays semiconductor technologies. The tautomerization of molecules, i.e., the bistable functional position of hydrogen protons within an organic frame, has recently been intensively discussed as a potential avenue towards nano-scale switches. It has been shown that tautomerization can be triggered locally or non-locally, i.e. by a scanning tunneling microscope (STM) tip positioned directly above or in close vicinity to the molecule...
July 21, 2017: Nano Letters
Juan Arturo Alanis, Dhruv Saxena, Sudha Mokkapati, Nian Jiang, Kun Peng, Xiaoyan Tang, Lan Fu, Hark Hoe Tan, Chennupati Jagadish, Patrick Parkinson
Single nanowire lasers based on bottom-up III-V materials have been shown to exhibit room-temperature near-infrared lasing, making them highly promising for use as nanoscale, silicon-integrable and coherent light sources. While lasing behavior is reproducible, small variations in growth conditions across a substrate arising from the use of bottom-up growth techniques can introduce inter-wire disorder, either through geometric or material inhomogeneity. Nanolasers critically depend on both high material quality and tight dimensional tolerances, and as such, lasing threshold is both sensitive to, and a sensitive probe of such inhomogeneity...
July 21, 2017: Nano Letters
Vinay Pathak, Ankush Prasad, Pavel Pospíšil
Singlet oxygen (1O2) is formed by triplet-triplet energy transfer from triplet chlorophyll to O2 via Type II photosensitization reaction in photosystem II (PSII). Formation of triplet chlorophyll is associated with the change in spin state of the excited electron and recombination of triplet radical pair in the PSII antenna complex and reaction center, respectively. Here, we have provided evidence for the formation of 1O2 by decomposition of protein hydroperoxide in PSII membranes deprived of Mn4O5Ca complex...
2017: PloS One
Georges Mion
: Ketamine's history begins in the 1950s in Detroit, Michigan, at Parke-Davis Laboratories. On 26 March 1956, Harold V. Maddox synthesised phencyclidine or PCP. Domino studied PCP effects in animals and in 1958, Greifenstein made the first trials of PCP in humans under the name of Sernyl. Sernyl did not cause depression of cardiovascular and respiratory functions, but elicited severe excitation with a very prolonged postoperative recovery. Because of its psychedelic effects, it became a street drug under the name of 'angel dust' and was placed on schedule II of Federal Controlled Substance Act (CSA) in 1978...
July 20, 2017: European Journal of Anaesthesiology
Alexandr Alekhin, Ilya Razdolski, Nikita Ilin, Jan P Meyburg, Detlef Diesing, Vladimir Roddatis, Ivan Rungger, Maria Stamenova, Stefano Sanvito, Uwe Bovensiepen, Alexey Melnikov
Using the sensitivity of optical second harmonic generation to currents, we demonstrate the generation of 250-fs long spin current pulses in Fe/Au/Fe/MgO(001) spin valves. The temporal profile of these pulses indicates ballistic transport of hot electrons across a sub-100 nm Au layer. The pulse duration is primarily determined by the thermalization time of laser-excited hot carriers in Fe. Considering the calculated spin-dependent Fe/Au interface transmittance we conclude that a nonthermal spin-dependent Seebeck effect is responsible for the generation of ultrashort spin current pulses...
July 7, 2017: Physical Review Letters
D Balaguer Ríos, K Aulenbacher, S Baunack, J Diefenbach, B Gläser, D von Harrach, Y Imai, E-M Kabuß, R Kothe, J H Lee, H Merkel, M C Mora Espí, U Müller, E Schilling, C Weinrich, L Capozza, F E Maas, J Arvieux, M A El-Yakoubi, R Frascaria, R Kunne, M Morlet, S Ong, J van de Wiele, S Kowalski, Y Prok
New measurements of the beam normal single spin asymmetry in the electron elastic and quasielastic scattering on the proton and deuteron, respectively, at large backward angles and at ⟨Q^{2}⟩=0.22  (GeV/c)^{2} and ⟨Q^{2}⟩=0.35  ( GeV/c)^{2} are reported. The experimentally observed asymmetries are compared with the theoretical calculation of Pasquini and Vanderhaeghen [Phys. Rev. C 70, 045206 (2004).PRVCAN0556-281310.1103/PhysRevC.70.045206]. The agreement of the measurements with the theoretical calculations shows a dominance of the inelastic intermediate excited states of the nucleon, πN and the Δ resonance...
July 7, 2017: Physical Review Letters
Julen Ibañez-Azpiroz, Manuel Dos Santos Dias, Benedikt Schweflinghaus, Stefan Blügel, Samir Lounis
We predict the existence of paramagnetic spin excitations (PSE) in nonmagnetic single adatoms. Our calculations demonstrate that PSE develop a well-defined structure in the meV region when the adatom's Stoner criterion for magnetism is close to the critical point. We further reveal a subtle tunability and enhancement of PSE by external magnetic fields. Finally, we show how PSE can be detected as moving steps in the dI/dV signal of inelastic scanning tunneling spectroscopy, opening a potential route for experimentally accessing electronic properties of nonmagnetic adatoms, such as the Stoner parameter...
July 7, 2017: Physical Review Letters
S Wüster
We show that Born-Oppenheimer surfaces can intrinsically decohere, implying loss of coherence among constituent electronic basis states. We consider the example of interatomic forces due to resonant dipole-dipole interactions within a dimer of highly excited Rydberg atoms, embedded in an ultracold gas. These forces rely on a coherent superposition of two-atom electronic states, which is destroyed by continuous monitoring of the dimer state through a detection scheme utilizing the background gas atoms. We show that this intrinsic decoherence of the molecular energy surface can gradually deteriorate a repulsive dimer state, causing a mixing of attractive and repulsive character...
July 7, 2017: Physical Review Letters
Assa Auerbach, Daniel P Arovas
For weakly disordered fractional quantum Hall phases, the nonlinear photoconductivity is related to the charge susceptibility of the clean system by a Floquet boost. Thus, it may be possible to probe collective charge modes at finite wave vectors by electrical transport. Incompressible phases, irradiated at slightly above the magnetoroton gap, are predicted to exhibit negative photoconductivity and zero resistance states with spontaneous internal electric fields. Nonlinear conductivity can probe composite fermions' charge excitations in compressible filling factors...
July 7, 2017: Physical Review Letters
Keisuke Matsuura, Hajime Sagayama, Amane Uehara, Yoichi Nii, Ryoichi Kajimoto, Kazuya Kamazawa, Kazuhiko Ikeuchi, Sungdae Ji, Nobuyuki Abe, Taka-Hisa Arima
We investigate the magnetic dynamics in the spinel-type vanadium oxide MnV_{2}O_{4}. Inelastic neutron scattering around 10 meV and a Heisenberg model analysis have revealed that V^{3+} spin-wave modes exist at a lower-energy region than previously reported. The scattering around 20 meV cannot be reproduced with the spin-wave analysis. We propose that this scattering could originate from the spin-orbital coupled excitation. This scattering is most likely attributable to V^{3+} spin-wave modes, entangled with the orbital hybridization between t_{2g} orbitals...
July 7, 2017: Physical Review Letters
Elvira R Sayfutyarova, Qiming Sun, Garnet Kin-Lic Chan, Gerald Knizia
We introduce the atomic valence active space (AVAS), a simple and well-defined automated technique for constructing active orbital spaces for use in multi-configuration and multi-reference (MR) electronic structure calculations. Concretely, the technique constructs active molecular orbitals capable of describing all relevant electronic configurations emerging from a targeted set of atomic valence orbitals (e.g., the metal d orbitals in a redcoordination complex). This is achieved via a linear transformation of the occupied and unoccupied orbital spaces from an easily obtainable single-reference wavefunction (such as from a Hartree-Fock or Kohn-Sham calculations) based on projectors to targeted atomic valence orbitals...
July 21, 2017: Journal of Chemical Theory and Computation
Alan Celestino, Alexander Eisfeld
We show that molecular aggregation can strongly influence the nonradiative decay (NRD) lifetime of an electronic excitation. As a demonstrative example, we consider a transition-dipole-dipole-interacting dimer whose monomers have harmonic potential energy surfaces (PESs). Depending on the position of the NRD channel ($q_{\rm nr}$), we find that the NRD lifetime ($\tau_{\rm nr}^{\rm dim}$) can exhibit a completely different dependence on the intermolecular-interaction strength. We observe that (i) for $q_{\rm nr}$ near the Franck-Condon region, $\tau_{\rm nr}^{\rm dim}$ increases with the interaction strength; (ii) for $q_{\rm nr}$ near the minimum of the monomer excited PES, the intermolecular interaction has little influence on $\tau_{\rm nr}^{\rm dim}$; (iii) for $q_{\rm nr}$ near the classical turning point of the monomer nuclear dynamics, on the other side of the minimum, $\tau_{\rm nr}^{\rm dim}$ decreases with the interaction strength...
July 21, 2017: Journal of Physical Chemistry. A
Mikkel Bregnhøj, Michael Westberg, Boris F Minaev, Peter R Ogilby
Singlet oxygen, O2(a(1)Δg), the lowest excited electronic state of molecular oxygen, is an omnipresent part of life on earth. It is readily formed through a variety of chemical and photochemical processes, and its unique reactions are important not just as a tool in chemical syntheses but also in processes that range from polymer degradation to signaling in biological cells. For these reasons, O2(a(1)Δg) has been the subject of intense activity in a broad distribution of scientific fields for the past ∼50 years...
July 21, 2017: Accounts of Chemical Research
Andreas Eichhöfer, Michael Kühn, Sergei Lebedkin, Max Kehry, Manfred M Kappes, Florian Weigend
A homologous series of three copper-tin-chalcogenide cluster molecules [Cu6E6(SnPh)2(PPh2Et)6] (E = S, Se, Te) was synthesized by reactions of CuO(O)CCH3 and PhSnCl3 with E(SiMe3)2 in the presence of PPh2Et. The cluster cage structures are similar, with slight differences in the bridging modes of the respective chalcogenide ligands E. The onset of the optical absorption displays a significant decrease of ca. 1.1 eV on going from sulfur to tellurium. The differences in bonding and electronic excitations can be rationalized by DFT and TDDFT calculations...
July 21, 2017: Inorganic Chemistry
Robert J Dillon, Leila Alibabaei, Thomas J Meyer, John M Papanikolas
The hole-injection and recombination photophysics for NiO sensitized with RuP ([Ru(II)(bpy)2(4,4'-(PO3H2)2-bpy)](2+)) are explored. Ultrafast transient absorption (TA) measurements performed with an external electrochemical bias reveal the efficiency for productive hole-injection, i.e. quenching of the dye excited state that results in a detectable charge-separated electron-hole pair, is linearly dependent on the electronic occupation of intragap states in the NiO film. Population of these states via a negative applied potential increases the efficiency from 0% to 100%...
July 21, 2017: ACS Applied Materials & Interfaces
Zsuzsanna Heiner, Thomas Roland, Jérémie Léonard, Stefan Haacke, Géza I Groma
When bound to a protein, the coenzyme NAD+/NADH typically exists in an extended conformation, while in aqueous solutions it can be characterized by an equilibrium of folded and unfolded structures. It was recognized long ago that in the folded conformation light absorption at the adenine ring initiates an effective energy transfer (ET) towards the nicotinamide group, but the mechanism of this process is still unexplored. Here we apply ultrafast transient absorption measurements on NADH combined with compartmental model analysis for following the kinetics of the ET...
July 21, 2017: Journal of Physical Chemistry. B
Wenhan He, Maksim Y Livshits, Diane A Dickie, Zhen Zhang, Luis E Mejiaortega, Jeffrey J Rack, Qin Wu, Yang Qin
We report the synthesis, characterization and detailed comparison of a series of novel Pt-bisacetylide containing conjugated small molecules possessing an unconventional "roller-wheel" shaped structure that is distinctly different from the "dumbbell" designs in traditional Pt-bisacetylide containing conjugated polymers and small molecules. The relationship between the chemical nature and length of the "rollers" and the electronic and physical properties of the materials are carefully studied by steady state spectroscopy, cyclic voltammetry, differential scanning calorimetry, single-crystal X-ray diffraction, transient absorption spectroscopy, theoretical calculation and device application...
July 21, 2017: Journal of the American Chemical Society
Tobias Meier, Rémy Pawlak, Shigeki Kawai, Yan Geng, Xunshan Liu, Silvio Decurtins, Prokop Hapala, Alexis Baratoff, Shi-Xia Liu, Pavel Jelinek, Ernst Meyer, Thilo Glatzel
Electron donor-acceptor molecules are of outstanding interest in molecular electronics and organic solar cells for their intramolecular charge transfer controlled via electrical or optical excitation. The preservation of their electronic character in the ground state upon adsorption on a surface is cardinal for their implementation in such single-molecule devices. Here, we investigate by atomic force microscopy and scanning tunneling microscopy a prototypical system consisting of a π-conjugated tetrathiafulvalene-fused dipyridophenazine molecule adsorbed on thin NaCl films on Cu(111)...
July 21, 2017: ACS Nano
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