I. A. Baranova

Direct visualization of the H-Xe bond in xenon hydrides: xenon isotopic shift in the IR spectra.

IR spectra of xenon hydrides (HXeCCH, HXeCC, and HXeH) obtained from different xenon isotopes ((129)Xe and (136)Xe) exhibit a small but detectable and reproducible isotopic shift in the absorptions assigned to H-Xe stretching (by 0.17-0.38 cm(-1)). To our knowledge, it is the first direct experimental evidence for the H-Xe bond in HXeY type compounds. The shift magnitude is in good agreement with quantum-chemical calculations.

Communication: Stabilization of radical anions with weakly bound electron in condensed media: A case study of diacetonyl radical anion

The radical anion resulting from electron capture by diacetonyl molecule has been characterized by EPR and optical absorption spectroscopy in glassy ether matrices at 77 K. In non-polar alkane glasses this species was not observed under the same conditions, which confirms the crucial role of matrix interactions in stabilizing this species. Calculations at the MP2 level show the vertical detachment energy to increase gradually from roughly zero for a bare anion to ∼1 eV for the complex involving six ether molecules.

Reactions of radical cations of acetals: Evidence for unimolecular decomposition

The thermal and photochemical reactions of the methylal radical cation /I/ in freon matrices were studied using selective deuteration for elucidating the structure of the resulting species. /I/ has been shown to decay by unimolecular reaction upon heating to 140 K as well as upon photolysis in CFCl3 matrix and the product of decay has been assumed to be the complex of formaldehyde radical cation with CFCl3. Such decay reaction has been demonstrated for 1,3-dioxolan radical cation as well.

The role of stable free radicals in the radiation-induced conductivity of low-density polyethylene

The radiation-induced conductivity (RIC) of low-density polyethylene (LDPE) under continuous irradiation with fast electrons (50 keV) was experimentally studied. The dose dependence of the concentration of stable paramagnetic centers was determined. The kinetics of RIC in LDPE was calculated on the basis of the Rose-Fowler-Vaisberg (RFV) model taking into account the buildup of radiation-induced traps. Good correlation between the experimental results and calculated data was found.

Positive hole transfer between organic molecules of different classes in freon matrices

The processes of positive charge (hole) transfer between organic molecules of different classes occurring upon irradiation of their frozen freonic solutions at 77 K were studied by ESR spectroscopy. The efficiency of positive hole transfer was characterized by the “redistribution coefficient”, which was determined as ratio of concentrations of the radical cations of different compounds at equal concentrations of the parent neutral molecules. A very effective positive hole transfer to toluene was shown to occur for alkane-toluene pairs (K > 10). Meanwhile, much lower K values (∼ 2 to 3) were observed for alkane-alkene pairs, in spite of a rather high difference in the ionization potentials (ca. 1 eV). This effect was explained by the conformation dispersion and distribution of environment configurations of ionized molecules for the alkane-alkene pairs. An effective positive hole transfer (K ∼ 6) was observed for the pair dimethyl ether-acetone, where the conformation dispersion was absent, although the difference in ionization potentials for this pair was only 0.3 eV.

Photochemistry of Ethylbenzene Radical Cations in Low-Temperature Freonic Matrices

Two different conformers of ethylbenzene radical cations (or a mixture of both conformers) can be stabilized in various freonic matrices. The first conformer retains the geometry of the parent molecule, whereas the second one corresponds to minimum energy. It was shown that the photochemical reactions of the radical cations in various freons at 77 K were not accompanied by a change in their conformational state. The spectral characteristics of ethylbenzene radical cations and the quantum yields of photoinduced charge transfer reactions were determined. The reasons for stabilization of different conformers of the radical cations in different freonic matrices are discussed.