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991.
Daniel Schiffbauer Claudia Wickleder Gerd Meyer Marco Kirm Michael Stephan Peter C. Schmidt 《无机化学与普通化学杂志》2005,631(15):3046-3052
The crystal structure, electronic states and VUV spectroscopic behaviour of Cs2KYF6 doped with Pr3+ ions have been investigated both by experimental and theoretical methods. Cs2KYF6 ( , Z = 4, a = 945.5(3) pm, R1all = 0.0297) crystallizes with the cubic elpasolite type of structure. The local relaxation of the activator ions in the host lattices has been calculated by the projector augmented wave method (computer code VASP). The electronic states have been calculated using a spin density functional procedure based on the atomic sphere approximation (computer code ASW). VUV spectroscopic measurements show fast 4f15d1 → 4f2 emission of nanosecond duration as well as slow 4f2 → 4f2 emission depending on the excitation energy which indicates the occupation of different sites in the host lattice. This assumption was verified by a recently developed quantum mechanical method. The combination of the experimental and the theoretical results show that the Pr3+ ions are occupying three different sites, namely the Y3+ and the Cs+ site as well as the K+ site. 相似文献
992.
E L Lebeau R A Binstead T J Meyer 《Journal of the American Chemical Society》2001,123(43):10535-10544
The kinetics of electron transfer for the reactions cis-[Ru(IV)(bpy)2(py)(O)]2+ + H+ + [Os(II)(bpy)3]2+ <==> cis-[Ru(III)(bpy)2(py)(OH)]2+ + [Os(III)(bpy)3]3+ and cis-[Ru(III)(bpy)2(py)(OH)]2+ + H+ + [Os(II)(bpy)3]2+ <==> cis-[Ru(II)(bpy)2(py)(H2O)]2+ + [Os(III)(bpy)3]3+ have been studied in both directions by varying the pH from 1 to 8. The kinetics are complex but can be fit to a double "square scheme" involving stepwise electron and proton transfer by including the disproportionation equilibrium, 2cis-[Ru(III)(bpy)2(py)(OH)]2+ <==> (3 x 10(3) M(-1) x s(-1) forward, 2.1 x 10(5) M(-1) x s(-1) reverse) cis-[Ru(IV)(bpy)2(py)(O)]2+ + cis-[Ru(II)(bpy)2(py)(H2O)]2+. Electron transfer is outer-sphere and uncoupled from proton transfer. The kinetic study has revealed (1) pH-dependent reactions where the pH dependence arises from the distribution between acid and base forms and not from variations in the driving force; (2) competing pathways involving initial electron transfer or initial proton transfer whose relative importance depends on pH; (3) a significant inhibition to outer-sphere electron transfer for the Ru(IV)=O2+/Ru(III)-OH2+ couple because of the large difference in pK(a) values between Ru(IV)=OH3+ (pK(a) < 0) and Ru(III)-OH2+ (pK(a) > 14); and (4) regions where proton loss from cis-[Ru(II)(bpy)2(py)(H2O)]2+ or cis-[Ru(III)(bpy)2(py)(OH)]2+ is rate limiting. The difference in pK(a) values favors more complex pathways such as proton-coupled electron transfer. 相似文献
993.
The oxidations of cis- and trans-[OsIII(tpy)(Cl)2(NH3)](PF6), cis-[OsII(bpy)2(Cl)(NH3)](PF6), and [OsII(typ)(bpy)(NH3)](PF6)2 have been studied by cyclic voltammetry and by controlled-potential electrolysis. In acetonitrile or in acidic, aqueous solution, oxidation is metal-based and reversible, but as the pH is increased, oxidation and proton loss from coordinated ammonia occurs. cis- and trans-[OsIII(tpy)(Cl)2(NH3)](PF6) are oxidized by four electrons to give the corresponding OsVI nitrido complexes, [OSVI(typ)(Cl)2(N)]+. Oxidation of [Os(typ)(bpy)(NH3)](PF6)2 occurs by six electrons to give [Os(tpy)(bpy)(NO)](PF6)3. Oxidation of cis-[OsII(bpy)2(Cl)(NH3)](PF6) at pH 9.0 gives cis-[OsII(bpy)2(Cl)(NO)](PF6)2 and the mixed-valence form of the mu-N2 dimer [cis-[Os(bpy)2(Cl)2[mu-N2)](PF6)3. With NH4+ added to the electrolyte, cis-[OsII(bpy)2(Cl)(N2)](PF6) is a coproduct. The results of pH-dependent cyclic voltammetry measurements suggest OsIV as a common intermediate in the oxidation of coordinated ammonia. For cis- and trans-[OsIII(tpy)(Cl)2(NH3)]+, OsIV is a discernible intermediate. It undergoes further pH-dependent oxidation to [OsVI(tpy)(Cl)2(N)]+. For [OsII(tpy)(bpy)(NH3)]2+, oxidation to OsIV is followed by hydration at the nitrogen atom and further oxidation to nitrosyl. For cis-[OsII(bpy)2(Cl)-(NH3)]+, oxidation to OsIV is followed by N-N coupling and further oxidation to [cis-[Os(bpy)2(Cl)2(mu-N2)]3+. At pH 9, N-N coupling is competitive with capture of OsIV by OH- and further oxidation, yielding cis-[OsII(bpy)2(Cl)(NO)]2+. 相似文献
994.
Fry HC Hoertz PG Wasser IM Karlin KD Meyer GJ 《Journal of the American Chemical Society》2004,126(51):16712-16713
Single wavelength excitation (lambdaex = 355 or 532 nm) of low-temperature stabilized (198 K) synthetic heme-dioxygen and heme-dioxygen/M complexes, where M = copper or iron in a non-heme environment, results in the dissociation of dioxygen as indicated by the generation of the ferrous heme (Soret band, 427 nm) and the bleaching of the ferric-superoxide (FeIII(O2-)) 410-nm Soret band in the transient absorption difference spectrum. Dioxygen rebinds to the four heme complexes studied with comparable rate constants ( approximately 6-9 x 105 M-1 s-1). However, the quantum yield for complete dissociation of O2 from our simplest heme-O2 complex (F8)FeIII(O2-) (phi = 0.60) is higher than the other complexes measured (phi = approximately 0.2-0.3) as well as that for oxy-myoglobin (phi = 0.3). 相似文献
995.
J. Hladký M. Novák A. Prokeš J. Votruba V. I. Genchev V. D. Kekelidze V. G. Krivokhizhin V. V. Kukhtin M. F. Likhachev I. Manno I. A. Savin L. V. Silvestrov G. Vesztergombi K. -F. Albrecht A. Meyer H. -E. Ryseck M. Sachwitz F. Deak 《Czechoslovak Journal of Physics》1976,26(11):1290-1293
New experimental results on the coherentK
L
0
C K
S
0
C regeneration in the momentum range 10p30 GeV/c are presented. For the quantity (f
0–¯f
0/k (where f0 and¯f
0 are theKC and¯K
0C forward scattering amplitudes andk is the wave number) we have obtained: arg (f
0–¯f
0)/k=–126±14 and ¦(f
0–¯f
0/k¦ p
–0.62±0.14 These results are well described by a simple Regge pole model including only the (-trajectory exchange in thet-channel with the intercept (0) close to 0.4.Presented at the IV International Symposium on High Energy and Elementary Particle Physics, Warszaw, September 1975. 相似文献
996.
997.
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999.
Berger C Fröhlich M Mönch H Nisius R Raupach F Schleper P Benadjal Y Blum D Bourdarios C Dudelzak B Eschstruth P Jullian S Lalanne D Laplanche F Longuemare C Paulot C Perdereau O Roy P Szklarz G Behr L Degrange B Minet Y Nguyen-Khac U Serri P Tisserant S Tripp RD Arpesella C Bareyre P Barloutaud R Borg A Chardin G Ernwein J Glicenstein JF Mosca L Moscoso L Becker J Becker KH Daum HJ Demski S Jacobi B Kuznik B Mayer R Meyer H Möller R Schubnell M Seyffert B Wei Y Wintgen P 《Physical review D: Particles and fields》1989,40(7):2163-2171
1000.