Spin density distribution in paramagnetic azafullerene

Hyperfine coupling (HFC) constants for ¹⁴N and ¹³C nuclei in azafullerene C₅₉N (1) were calculated. The HFC constants for the ¹H and ¹³C nuclei in the ^·CH₃ radical were calculated as functions of the pyramidal distortion of the angles at the carbon atom. Using this angular dependence, the spin density distribution of the unpaired -electron in 1 was determined. The spin density of the unpaired -electron in 1 is mainly localized around the nitrogen atom.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2372–2374, November, 2004.     

Experimental testing of molecular dynamic functions of pairs by the isotope selectivity of radical recombination

A method for experimental testing of the molecular dynamic functionf(t), which describes the generation of reencounters in a dynamic pair of molecular particles, has been developed. The method is based on the analysis of isotope separation in spin selective reactions of a radical pair. Thef(t) function derived from the solution of the diffusion equation with physically rigorous initial and boundary conditions describes experimental results much better than the well-known Noyes function. Conditions that make it possible to increase the efficiency of isotope separation in spin selective reactions are formulated.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1639–1645, September, 1995.This work was financially supported by the Russian Foundation for Basic Research (Project No. 93-03-05227).     

NMR in paramagnetic complexes of radicals with organic ligands. II. Method of identification of electronic structure of complexes — Theory

A method of identification of the electronic structure of stable nitroxide radical complexes with organic ligands is developed. The idea of this approach is that the concentration dependences of the paramagnetic shifts and line widths of the NMR spectra of two ligands in solution depend on whether these ligands form complexes with the same radical orbital or with different orbitals. In the latter case the complexation of one ligand should not influence the paramagnetic shift and line broadening of another ligand molecule present in the solution. In contrast, in the former case such influence should exist since both ligands are in competition. On this basis different schemes of complexation are considered and theoretical expressions for paramagnetic shifts and line widths are derived that show what kind of experimental data is required to identify the structure of the complex. The theory developed can be generalized to other paramagnetic complexes of radicals, ions and molecules.     

Heteroorganic metal-containing paramagnetic and ferromagnetic polymers. 2. Investigation of thermal condensation of polymetalloorganosiloxanes

Products of the thermal condensation of polymetalloorganosiloxanes in an inert atmosphere are hydrocarbons formed by detachment of organic groups from the silicon atom. Some of the organic groups remain in the pyrolyzed residue in the form of polyaromatic nuclei and silphenylene fragments (for polymetallophenyl-siloxanes). The pyrolysis residue also contains reduced forms of the metal, carbides and carbide-suicides of the metal, and silicon dioxide. Radical process schemes are proposed for an explanation of the formation of hydrocarbons, reduced forms of the metal, and silicon dioxide in the course of thermal condensation of polymetalloorganosiloxanes.For previous communication, see [1].Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 600–605, March, 1991.     

Magnetic field effects on the initiation of chain oxidation

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Dynamics and mechanism of the non-adiabatic transitions from the ungerade I2(D0+u) state induced by collisions with rare gas atoms

The stepwise three-photon two-color laser excitation scheme is used for selective population of the first-tier ion-pair D0(+)(u) state of molecular iodine. Collection and analysis of the luminescence after the excitation of the v(D) = 6, 8, 13 and 18 vibronic levels of the D state in the pure iodine vapor and the gas-phase mixtures with He, Ar and Xe provide the total and, whenever possible, partial rate constants for the collision-induced non-adiabatic transitions to the other ion-pair states of the first tier. Comparison with the analogous data obtained previously for the non-adiabatic transitions from the E0(+)(g) state reveals the similarity between two cases. For He, the D ? E transitions are preferable, whereas for Ar and Xe transitions to the D' and β states dominate at v(D) = 6, 8 and 13, in accord with the statistical considerations. Efficient population of the δ state at v(D) = 18 in Ar and Xe is the most prominent non-statistical feature observed. The vibrational product state distributions for the D → E transitions are also obtained. In contrast to the previously studied E → D transition, they show significant positive vibronic energy transfer. The measurements for He and Ar are accompanied by the quantum scattering calculations that reproduce well the main qualitative features of the experimental results.     

Magnetic isotope effect in the photolysis of organotin compounds

Photolysis of organotin molecules RSnMe3 is shown to be a spin selective radical reaction accompanied by fractionation of magnetic, (117,119)Sn, and nonmagnetic, (118,120)Sn, isotopes between starting reagents and products. A primary photolysis process is a homolytic cleavage of the C-Sn bond and generation of a triplet radical pair as a spin-selective nanoreactor. Nuclear spin dependent triplet-singlet conversion of the pair results in the tin isotope fractionation. Experimentally detected isotope distribution unambiguously demonstrates that the classical, mass-dependent isotope effect is negligible in comparison with magnetic, spin-dependent isotope effect.