ESR spectra were recorded in the X-band (9.6GHz) and in the W-band (94GHz)

and electron spin relaxation was measured by electron spin echo at 4.2 to 300K for

radicals in natural calcite samples. Four types of carbonate radical spectra and two

sulfate radical spectra were identified and high accuracy g-factors were derived.

Time and temperature behaviour of the spectra showed that the predominant CO2

−

radicals were rigidly bonded or underwent free reorientation, whereas CO3

−, SO2

−

and SO3

− only underwent free reorientation. Below 200K the free reorientation of

CO2

− was suppressed and a hindered rotation around a single local axis appeared.

The electron spin echo-detected spectrum proved that the lines of free rotating

radicals were homogeneously broadened, thus they could not participate in electron

spin echo formation. Spin–lattice relaxation data showed that CO2

− radicals were

decoupled from lattice phonons and relaxed via local mode tunnelling motion

between inequivalent oxygen positions of CO2

− molecules. The tunnelling

appeared in two excited vibrational states of energy 71 and 138/cm. Librational

motions of CO2

− molecules were detected by electron spin echo decay (phase

relaxation) with energy, 153/cm. Two kinds of impurity hydrogen atoms were

distinguished from ESEEM: in-water inclusions and water coordinated to the

calcium ions.

Dynamics of CO2

− Radiation Defects in Natural Calcite Studied by ESR, Electron

Spin Echo and Electron Spin Relaxation. M.Wencka, S.Lijewski, S.K.Hoffmann:

Journal of Physics - Condensed Matter, 2008, 20[25], 255237