L.C. Brunel

EPR spectroscopy at very high field

Abstract A very high field EPR spectrometer, which can operate at magnetic fields up to 19 T, has been constructed. The first EPR spectra of a nitroxide free radical in solution are reported. A discussion of the applications of high frequency EPR (corresponding to the far infrared) is presented.

Millimeter band EPR spectra reveal large zero-field splittings in copper(II)—semiquinonato complexes

Abstract The magnetic interaction between copper(II) and ortho-semiquinones has been investigated by the EPR technique using a spectrometer operating in the millimeter-wavelength range. The polycrystalline-powder EPR spectrum of [Cu(Me 3 [12]N 3 )-(DTBSQ)]ClO 4 (Me 3 [12]N 3 = 2,4,4-trimethyl-1,5,9-triazacyclododec-1-ene; DTBSQ = 3,5-di- t -butyl- o -semiquinonato) recorded at 4.2 with an exciting frequency of 8.17 cm −1 , is typical of a spin triplet with a large zero-field splitting (ZFS). The ZFS parameters have been obtained directly from the spectrum using the Wasserman equations. Both dipolar and exchange contributions to the ZFS are discussed within a molecular-orbital framework.

Very high field and multifrequency ESR study of a coal sample

Abstract The ESR spectra of a coal sample have been obtained at very high fields (8.837 T, 12.805 %, 15.715 T). The linewidth values, as compared to those obtained at lower field, allow one to assign numerical values to the g factor dispersion and to the spin-exchange frequency.

High field electron spin resonance

Abstract Recent developments of the high field spectroscopy are reviewed. The application of this technique to various fields of condensed matter physics and chemistry reveal interesting and new results on the local and dynamical character of paramagnetic entities.

Very high field EPR study ofcis- andtrans-polyacetylene

Some neutralcis- andtrans-polyacetylene samples have been studied at 30–0.7 mm wave band EPR. A higher spectral resolution allows one to determine the principal values of anisotropicg-tensor of localized paramagnetic centers in polyacetylene, attributed to pinned neutral solitons. The Very High Frequency EPR allows us to observe the increase of a number of such centers and the appearance of soliton diffusion along the polymer chains after thecis-trans isomerization.

Recent developments in high field CW ESR spectroscopy

Abstract Recent developments in high magnetic field/high-frequency CW ESR spectroscopy are reviewed. The application of this technique to Solid State Physics is illustrated by results obtained with one-dimensional antiferromagnets which demonstrate the needs for both high magnetic fields and high frequencies and by results concerning high Tc superconductors which show the interest of the increase in resolution due to the use of high fields.

Study of neutral polyacetylene by multifrequency EPR method

Summary form only given. A great number of EPR studies of polyacetylene (PA) was performed at /spl lambda/ /spl ges/ cm wavebands EPR during the last years. However, the low spectral resolution and strong cross relaxation processes do not allow one to separate the lines of paramagnetic centers of different mobility at this wavelength range. This leads to ambiguity of the data concerned with soliton dynamics and content of mobile solitons in trans-PA. In order to obtain more correct and complete information, neutral cis- and trans-PA samples have been studied in 30-0.7-mm wave length range EPR. A higher spectral resolution allows one to determine the main values of g-tensor of localized paramagnetic centers in as-prepared cis-PA, which were attributed to neutral solitons pinned on short trans-PA segments. The cis-trans-isomerization induces the increase of a number of such centers and the appearance of /spl sim/6% solitons fast diffusing along the polymer chains. The /spl Delta/H/sup mob//spl sim/(/spl Delta/H/sup loc/)/sup i.3/ dependency obtained for the linewidths of mobile and localized solitons also evidences the existence of 1D soliton diffusion in trans-PA. Another dependency, /spl Delta/H/sup loc/ /spl equiv/ /spl lambda//sup -2/ indicates the sufficient decrease of a cross-relaxation rate at magnetic fields H/spl ges/1.2 T.

High-field EPR spectroscopy of thermal donors in silicon

Abstract Si-NL10 thermal donors were investigated by high-field electron paramagnetic resonance in an experimental set-up consisting of a pumped far-infrared laser operating in the 350 GHz frequency range and a superconducting coil. The experiment was conducted at a magnetic field of about 12 T. Under these conditions the first direct experimental evidence for the multispecies character of the Si-NL10 thermal donor centres has been obtained.