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781.
Lever L Hu Y Myronov M Liu X Owens N Gardes FY Marko IP Sweeney SJ Ikonić Z Leadley DR Reed GT Kelsall RW 《Optics letters》2011,36(21):4158-4160
We report modulation of the absorption coefficient at 1.3?μm in Ge/SiGe multiple quantum well heterostructures on silicon via the quantum-confined Stark effect. Strain engineering was exploited to increase the direct optical bandgap in the Ge quantum wells. We grew 9?nm-thick Ge quantum wells on a relaxed Si0.22Ge0.78 buffer and a contrast in the absorption coefficient of a factor of greater than 3.2 was achieved in the spectral range 1290-1315?nm. 相似文献
782.
Desloge JG Reed CM Braida LD Perez ZD Delhorne LA 《The Journal of the Acoustical Society of America》2011,129(6):3884-3896
A functional simulation of hearing loss was evaluated in its ability to reproduce the temporal modulation transfer functions (TMTFs) for nine listeners with mild to profound sensorineural hearing loss. Each hearing loss was simulated in a group of three age-matched normal-hearing listeners through spectrally shaped masking noise or a combination of masking noise and multiband expansion. TMTFs were measured for both groups of listeners using a broadband noise carrier as a function of modulation rate in the range 2 to 1024 Hz. The TMTFs were fit with a lowpass filter function that provided estimates of overall modulation-depth sensitivity and modulation cutoff frequency. Although the simulations were capable of accurately reproducing the threshold elevations of the hearing-impaired listeners, they were not successful in reproducing the TMTFs. On average, the simulations resulted in lower sensitivity and higher cutoff frequency than were observed in the TMTFs of the hearing-impaired listeners. Discrepancies in performance between listeners with real and simulated hearing loss are possibly related to inaccuracies in the simulation of recruitment. 相似文献
783.
Copper carbonyl cations of the form Cu(CO)(n)(+) (n = 1-8) are produced in a molecular beam via laser vaporization in a pulsed nozzle source. Mass-selected infrared photodissociation spectroscopy in the carbonyl stretching region is used to study these ions and their argon "tagged" analogues. The geometries and electronic states of these complexes are determined by the number of infrared-active bands, their frequency positions, and their relative intensities compared to the predictions of theory. Cu(CO)(4)(+) has a completed coordination sphere, consistent with its expected 18-electron stability. It also has a tetrahedral structure similar to that of its neutral isoelectronic analog Ni(CO)(4). The carbonyl stretch in Cu(CO)(4)(+) (2198 cm(-1)) is blue-shifted with respect to the free CO vibration (2143 cm(-1)), providing evidence that this is a "non-classical" metal carbonyl. 相似文献
784.
Mehraeen S Kulkarni A Chi M Reed BW Okamoto NL Browning ND Gates BC 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(3):1000-1008
The structures of small, robust metal clusters on a solid support were determined by a combination of spectroscopic and microscopic methods: extended X‐ray absorption fine structure (EXAFS) spectroscopy, scanning transmission electron microscopy (STEM), and aberration‐corrected STEM. The samples were synthesized from [Os3(CO)12] on MgO powder to provide supported clusters intended to be triosmium. The results demonstrate that the supported clusters are robust in the absence of oxidants. Conventional high‐angle annular dark‐field (HAADF) STEM images demonstrate a high degree of uniformity of the clusters, with root‐mean‐square (rms) radii of 2.03±0.06 Å. The EXAFS Os? Os coordination number of 2.1±0.4 confirms the presence of triosmium clusters on average and correspondingly determines an average rms cluster radius of 2.02±0.04 Å. The high‐resolution STEM images show the individual Os atoms in the clusters, confirming the triangular structures of their frames and determining Os? Os distances of 2.80±0.14 Å, matching the EXAFS value of 2.89±0.06 Å. IR and EXAFS spectra demonstrate the presence of CO ligands on the clusters. This set of techniques is recommended as optimal for detailed and reliable structural characterization of supported clusters. 相似文献
785.
The bidentate phosphine 2,11-bis(diphenylphosphinomethyl)benzo [c]phenanthrene ( 1 ) has been used to prepare the mononuclear, square planar complexes trans-[MX(CO)( 1 )] and trans-[M(CO)(CH3CN)( 1 )][BF4] (M = Rh, Ir; X = Cl, Br, I, NCS). It is found that the tendency of these complexes to form adducts with CO, O2 and SO2 is significantly lower than that of the corresponding Ph3P complexes. The oxidative-addition reactions of complexes trans-[IrX (CO) ( 1 )] with hydrogen halides give the six-coordinate species [IrHX2(CO) ( 1 )]. The complexes [IrH2I (CO) ( 1 )] and [IrH2L (CO) ( 1 )] [BF4] (L = CO and CH3CN) have been obtained from hydrogen and the corresponding substrates. The model compounds trans-[MCl (CO) (Ph2PCH2Ph)2] (M = Rh, Ir), trans-[Ir (CO) (CH3CN) (Ph2PCH2Ph)2] [BF4], [IrHCl2(CO)(Ph2PCH2Ph)2] and [IrH2(CO)2(Ph2PCH2Ph)2] [BF4] have been prepared and their special parameters are compared with those of the corresponding complexes of ligand 1 . The influence of the static requirements of this ligand on the chemistry of its rhodium and iridium complexes is discussed. 相似文献
786.
Andrei V. Bordunov Jerald S. Bradshaw Victor N. Pastushok Xian X. Zhang Xiaolan Kou N. Kent Dalley Zhaoxia Yang Paul B. Savage Reed M. Izatt 《Tetrahedron》1997,53(52):808-17606
A simple synthetic pathway for the preparation of oxime- and Schiff base-containing aza- and diazacrown ethers is reported. N-Methoxymethyl-substituted aza-15-crown-5 and aza-18-crown-6 as well as N,N′-bis(methoxymethyl)-substituted diaza-18-crown-6 were treated with 5-bromosalicylaldehyde to produce the N-(2′-hydroxy-3′-carbonyl-5′-bromobenzyl)-substituted aza-15-crown-5 (8), aza-18-crown-6 (9) and N,N′-bis(2′-hydroxy-3′-carbonyl-5′-bromobenzyl)-substituted diaza-18-crown-6 (10) compounds. Compounds 8 and 10 were treated with hydroxylamine to give oxime-substituted ligands 12 and 13. A series of bis-Schiff base-containing diaza-18-crown-6 ligands were prepared by reacting 10 with 2-hydroxyaniline (to form 14), 5-nitro-2-hydroxyaniline (15), 2-aminopyridine (16), 2-hydrazinopyridine (17) and N-aminomorpholine (18). Compounds 12–18 are potential complexing agents for simultaneous binding of soft transition and hard alkali or alkaline earth metal ions in one molecule. These new oxime- and Schiff base-containing ligands interacted strongly with Na+ and K+ in methanol. The interaction of the aromatic portions of 9, 10, and 12–15 with transition metal ions was shown by the UV spectra of the metal ion complexes in 50% aqueous DMF. The X-ray structure of 10 is reported. 相似文献
787.
Aiguo Li Zhijun Zhang Yangjie Wu Haoyun An Reed M. Izatt Jerald S. Bradshaw 《Journal of inclusion phenomena and macrocyclic chemistry》1993,15(4):317-327
Five new bis(benzo-15-crown-5) derivatives with different connecting groups were synthesized. Potassium ion-selective PVC membrane electrodes based on these bis(crown ether)s were prepared and their selective properties were measured. The results showed that most of these electrodes are stable over a wide pH range and their selectivity coefficients were better than those of an electrode based on natural valinomycin. 相似文献
788.
Amy Avelar Fook S. Tham Christopher A. Reed Prof. Dr. 《Angewandte Chemie (International ed. in English)》2009,48(19):3491-3493
Acid remarks : The anhydrous diprotic boron acids H2(B12X12) (X=Cl, Br; see picture, B orange, X green) are the first examples of diprotic superacids and may be the strongest acids yet isolated. Both protons protonate benzene to give benzenium ion salts that are stable at room temperature. These acids owe their existence to the stability of the icosahedral B12 cluster with its dinegative charge buried beneath a layer of halide substituents.
789.
Yangjie Wu Haoyun An Jingchao Tao Jerald S. Bradshaw Reed M. Izatt 《Journal of inclusion phenomena and macrocyclic chemistry》1990,9(3):267-274
Complexes of nine 4'-substituted benzo-15-crown-5 ligands with sodium picrate were prepared. A good linear relationship of the . values from the UV spectra and Hammett [p - m] values was observed. Charge transfer complexes of ten 4'-substituted benzo-l5-crown-5 ligands with picric acid were isolated in crystalline form. The color of the complexes depended on the nature of the substituents. All of the complexes were identified by elemental analyses, UV and IR spectra. 相似文献
790.
Stoyanov ES Stoyanova IV Tham FS Reed CA 《Journal of the American Chemical Society》2008,130(36):12128-12138
The nature of H(H2O)n(+) cations for n = 3-8 with weakly basic carborane counterions has been studied by IR spectroscopy in benzene and dichloroethane solution. Contrary to general expectation, neither Eigen-type H3O x 3 H2O(+) nor Zundel-type H5O2(+) x 4 H2O ions are present. Rather, the core species is the H7O3(+) ion. 相似文献