Resonant light delay in GaN with ballistic and diffusive propagation

We report on a strong delay in light propagation through bulk GaN, detected by time-of-flight spectroscopy. The delay increases resonantly as the photon energy approaches the energy of a neutral-donor bound exciton (BX), resulting in a velocity of light as low as 2100 km/s. In the close vicinity of the BX resonance, the transmitted light contains both ballistic and diffusive components. This phenomenon is quantitatively explained in terms of optical dispersion in a medium where resonant light scattering by the BX resonance takes place in addition to the polariton propagation.     

Ynaziridines. Methods of synthesis of a new type of ynamines

Ways of synthesizing ynaziridines by successive halogenation and dehydrohalogenation of enaziridino esters, the reaction of potassium aziridinide with bromophenylacetylene, the reaction of 1H-aziridines with the methyl ester of bromopropionic acid was studied. The different direction of the reaction of aziridines with bromomethylpropiolate as a function of the nature of the solvent was demonstrated. In methanol the addition of aziridine to the triple bond proceeds stereospecifically with the formation of the E-isomer. When this reaction was conducted in ether, ynaziridines were obtained for the first time. An effective method of synthesis of ynaminoesters was developed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1492–1496, November, 1984.     

Synthesis of the cationic complexes [(C5H4CPh2)2Ru]2+ and [Ph2(HO)CC5H4RuC5H4CPh2]+. Molecular and crystal structures of [Ph2(HO)CC5H4RuC5H4CPh2]+[CF3SO3]− · CHCl3 and [C5H5RuC5H4CPh2]+PF6 −

The formation of the previously unknown [(C₅H₄CPh₂)₂Ru]²⁺ dication was established by¹H and¹³C NMR spectroscopy. This cation readiiy hydrolizes to form the monocation, [Ph₂(HO)CC₅H₄RuC₅H₄CPh₂]⁺. The latter was characterized by NMR spectroscopy and X-ray structural analysis. For comparison, [C₅H₅RuC₅H₄CPh₂]⁺PF₆ ^? was also studied by X-ray structural analysis. The increase in the M-C_α distance and the decrease in the angle of inclination of the CPh₂ group to the metal atom in disubstituted ruthenocene compared to those in monosubstituted ruthenocene is related to the presence of a bulky substituent in the second Cp ligand and is likely due to the crystal packing effect. IR spectra and X-ray structural analysis attest to the existence of the OH ? OSO₂CF₃ hydrogen bond in crystals of the trifluoromethanesulfonate monocation.     

Hydrogen bonds and protonation of carbonyl-containing polynuclear rhodium complexes

According to IR spectroscopy data, the interaction of bi-, tri-, and tetranuclear cyclopentadienylcarbonyl rhodium complexes with rather weak protic acids (phenols, fluoroalcohols) in low-polarity media results in the formation of hydrogen bonds of the OH...O=C type with bridged carbonyl groups. According to¹H NMR data, protonation of these complexes with strong acids (CF₃COOH and HBF₄) occurs at the the Rh-Rh bond to give the symmetrical bridge.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 386–388, February, 1995.This work was carried out with the financial support of the Russian Foundation for Basic Research (Project No. 93-03-0461).     

Morphology of (001) and (110) surfaces of crystal layers in solid solutions of II–VI compounds with a high ZnSe content under atmospheric conditions

The atomic-force microscopy is used for studying the effect of atmospheric conditions on the morphology of (001) growth surfaces and (110) cleavage planes of layers in II–VI compounds with a high ZnSe content. It is proved directly for the first time that the formation of nanoclusters on these surfaces is accompanied by corrosion of the entire surface due to the accumulation of corrosion products. The corrosion of the surface attains saturation even at a depth of a few (2–3) monolayers, which constrains the total volume of nanoclusters on the surface. A further increase in the size of nanoclusters with time occurs due to a decrease in their number. The corrosion depth can locally increase significantly in the surface regions with considerable internal stresses; in particular, corrosion can evolve deep inside the stressed interfaces in instrumental structures.     

Resonance energy transfer in a dense array of II–VI quantum dots

Förster resonance energy transfer in inhomogeneous dense arrays of epitaxial CdSe/ZnSe quantum dots is demonstrated by time- and space-resolved photoluminescence spectroscopy. The specific feature of this process is the dipole–dipole interaction between the ground exciton levels of small quantum dots and the excited levels of large dots. This interaction brings efficient energy collection and spectral selection of a limited number of emitters. Results of theoretical modeling of optical transitions in spheroidal quantum dots with a Gaussian potential profile agree with the observed features of optical spectra induced by the change of the dominant energy transfer mechanism.     

Reactions of carbonylmetallate anions with 1-haloalkynes

The main regularities of the reactions of 1-haloalkynes RC≡CX with carbonylmetallate anions [(η⁵-C₅R′₅)(CO)₃M]⁻ (R′ = H (1–3),, M=Cr (1), M=Mo (2), or M=W (3); R′ =Me (4–6), M=Cr (4), M=Mo (5), or M=W (6) were revealed. It was established that the first stage of the reactions of anions1–6 with bromo- or iodoalkynes RC≡CX (X=Br or I) involved the transfer of the halogen atom from the sp-hybridized carbon atom to the transition metal atom to form carbonyl halides [(η⁵-C₅R′₅)(CO)₃MX. To the contrary, the reactions of anions1–6 with chloroalkynes RC≡CCl proceeded selectively as a nucleophilic substitution at the unsaturated carbon atom, the reaction rate being governed by the nucleophilicity of the carbonylmetallate anions and the electron-withdrawing ability of the R group. These reaction paths are consistent with the structures of the lowest unoccupied molecular orbitals (LUMO) in the PhC≡CX molecules (X=Cl, Br, or I) calculated by the MNDO/PM3 method. In the case of the reactions of 1-chloroheptyne-1 C1C≡CC₅H₁₁ ⁿ, anions1–3 appeared to be insufficiently nucleophilic, but these reactions can be performed as cross-coupling of the carbonylmetallate anions with chloroalkynes catalyzed by palladium complexes. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1176–1184, June, 1999.