V. F. Yudanov

Electron spin echo envelope modulation of trapped radicals in disordered glassy systems: Application to the molecular structure around excess electrons in γ‐irradiated 2‐methyltetrahydrofuran glass

Three specifically deuterated 2‐methyltetrahydrofurans (MTHF) have been synthesized to delineate the proton (deuteron) arrangement and hence the molecular arrangement around a trapped excess electron in γ‐irradiated glassy MTHF at 77 K. The electron–deuteron anisotropic hyperfine interaction was detected by its modulation of the two‐pulse electron spin echo envelope. Comparison of experimental and simulated modulation patterns shows that the excess electron is located about 3.7 A below the center of the plane of the ring carbons in MTHF on the side opposite the methyl group and that three or four MTHF molecules constitute the first solvation shell. A second moment analysis of the EPR linewidths of the excess electron in the variously deuterated MTHF’s independently supports the same structural conclusions. The shortest electron–proton distance is then ∼3.1 A, which compares moderately well with previous, less accurate ENDOR results. This structure seems somewhat more expanded than that indicated by theore...

Electron spin echo envelope modulation of trapped radicals in disordered glassy systems: Application to the molecular structure around excess electrons in γ‐irradiated 10M sodium hydroxide alkaline ice glass

Electron spin echo signals associated with trapped electrons in aqueous matrices show a modulation due to hyperfine interaction with the surrounding magnetic nuclei. The three pulse electron spin echo modulation gives information about the next nearest neighbor deuterons surrounding the electron. Analysis of the phase change in the three pulse modulation gives an effective deuteron interaction distance of 3.6 A. The two pulse spin echo modulation depends on both the nearest and next nearest neighbor deuterons. Simulations of this modulation support a structural model in which the number of equivalent nearest neighbor deuterons to the electron is 6 at a distance of 2.1 A and with an isotropic coupling constant of 0.9 MHz (5.8 MHz for protons). The orientation of the water molecules in the first solvation shell is not uniquely determined and two possible models are proposed. In model I there are three first solvation shell water molecules with their molecular dipoles oriented toward the electron so that the...

Electron spin-echo studies of weak hyperfine interactions with ligands in some VO2+ complexes in frozen glassy solutions

Abstract Methods of envelope modulation function calculations in the case of paramagnetic centers having an axially symmetric g factor are described. Parameters of the hyperfine interactions between unpaired electrons of VO2+ ions and molecular deuterons have been obtained from the analysis of envelope modulation patterns for the two- and three-pulse electron spin echo of VO2+ complexes with D2O, CH3OD, and CD3OH. On this basis structural parameters of the first coordination sphere of VO2+ complexes with water and methyl alcohol have been determined.

Modulation effects in the electron spin echo of biradical systems

The results of a theoretical and experimental investigation of the modulation effects in the electron spin echo of biradical systems are presented. SO4−radicals stabilized as pairs in UV-irradiated potassium persulfate and frozen solutions of the stable N,N′-[bis-(α, α-diphenylpicrylhydrazyl)-Β-picryl-3]-piperazine biradical (A) were chosen as models. The modulation effects in the ESE of SO4−radicals in potassium persulfate are shown to be caused by a dipole-dipole interaction between the radicals. The results of the study of the ESE of the A-biradicals leads to the assumption that the observed modulation effects are caused by an exchange interaction between unpaired electrons.

Electron spin echo of CH2OH radicals adsorbed in A-type zeolites

Abstract Data on the trapping site of radicals in zeolite α-cages have been obtained by the analysis of modulation effects in the electron spin echo of CH 2 OH radicals produced by irradiation in A-type zeolite with adsorbed methyl alcohol.

Modulation effects in the spin-echo signals of CH(COOH)2 radicals

Results are given on the angular dependence of these effects for radicals stabilized in a γ-irradiated single crystal of malonic acid. The modulation is ascribed to anisotropic hyperfine interaction with the α proton of CH(COOH)2. The results allow electron spin echo to be used in certain cases to measure small splittings in the ESR spectra of free radicals.

Weak Hyperfine Interactions in VO 2+ — Water, Methanol Complies Studied by the Electron Spin Echo Method in Frozen Glassy Solutions

Parameters of the hfi between unpaired electrons in VO2+ and molecular deuterons have been obtained from the analysis of envelope modulation patterns for the ESE of VO complexes with D2O, CH3OD and CD3OH. Structural parameters of the first coordination sphere of the above complexes have been determined. Methods of envelope modulation function calculations for paramagnetic centers with axially symmetric g-factor are described.