Multifrequency EPR study on radiation induced centers in calcium carbonates labeled with ¹³C

Abstract

Abstract. In calcite and aragonite, -irradiated at 77 K, several paramagnetic centers were generated and detected by EPR spectroscopy; in calcite, CO 3 -(orthorhombic symmetry, bulk and bonded to surface), CO 3 C more detailed information about the formed radicals was possible to be obtained. In both natural (white coral) and synthetic aragonite the same radicals were identifi ed with main differences in the properties of CO 2 -radicals. An application of Q-band EPR allowed to avoid the signals overlap giving the characteristics of radical anisotropy.

Nanoscale Effects of Radiation (UV, X-ray, and γ) on Calcite Surfaces: Implications for its Mechanical and Physico-Chemical Properties

“…Concentration of the electrons remaining in traps, proportional to the integral intensity of an electron paramagnetic resonance (EPR) signal of paramagnetic species, grows with the dose of absorbed radiation (which is relevant for dosimetry) and therefore the time of exposure (relevant for dating). Several types of paramagnetic species, also known as radiation defects, can be generated in calcite as a result of interaction of carbonate ion CO 3 2– with incident radiation, including CO 2 – , CO 3 – , and CO 3 3– defects with orthorhombic, axial, or isotropic symmetry, ,,,− and defects related to impurity anions such as sulfides, nitrates, or phosphorates. ,,,,, …”

Enhancing Hydrogen Cluster Storage in Clathrate Hydrates via Defect-Mediated Lattice Engineering

“…Surprisingly, in the case of [THF+CH 4 ]*, OH • (a­(H) = 1.5 mT) as well as CH 3 • (a­(H) = 2.3 mT) with tetrahydrofuran-2-yl, tetrahydrofuran-3-yl, and H • radicals were observed, which did not appear in the other cases. Note that the experimentally obtained spectra matched the simulated spectra well; the refined values of the experimental hyperfine coupling constants and g factors of each radical for tetrahydrofuran-2-yl (H­(α) = 1.47, 2H­(β) = 3.4, 2H­(γ) = 1.93, 2H­(γ′) = 0.35 mT), tetrahydrofuran-3-yl (H­(α) = 2.42, 2H­(β) = 0.46, 2H­(β′) = 0.46 mT), H • (a­(H) = 51.69 mT), CO 2 –• ( g = 2.0006 mT), OH • ( g = 1.9974 mT), and CH 3 • (a­(H) = 2.335 mT) also showed good agreement with the values reported in the literature. ,,− …”

“…In [THF+CO 2 ]*, hydrogen radicals were not detected, and the intensities of the five peaks of the hyperfine structure significantly differed from [THF]* and [THF+H 2 ]*. Considering the centered peak, the tetrahydrofuran-2-yl, tetrahydrofuran-3-yl, CO 2 –• ( g = 2.0006), and HOCO • ( g = 2.0001) radicals were detected, but H • from THF was not observed in the [THF+CO 2 ]*. Surprisingly, in the case of [THF+CH 4 ]*, OH • (a­(H) = 1.5 mT) as well as CH 3 • (a­(H) = 2.3 mT) with tetrahydrofuran-2-yl, tetrahydrofuran-3-yl, and H • radicals were observed, which did not appear in the other cases.…”

Radiation Defects in Lime Mortars and Plasters Studied by EPR Spectroscopy

“…Both γand UV-irradiation induced two main overlapping signals in Hippos samples, shown as simulated lines in Figure 2g-a triplet resulting from hyperfine structure (I = 1), with parameters g x = g y = 2.0060, g z = 2.0019, A x = A y = 3.40 mT, A z = 6.80 mT, and an orthorhombic signal with g x = 2.0029, g y = 2.0014, g z = 1.9971. While the latter is a well-known signal connected with CO 2 paramagnetic center (Ikeya 1993(Ikeya , 2004Callens et al 1998;Bartoll et al 2000), the triplet is assigned by several authors to NO 3 2ion (Eachus and Symons 1968;De Cannière et al 1988;Sato et al 2004;Kundu et al 2005;Sadło et al 2015). Additionally, a wide, isotropic, Figure 2 EPR spectra of UV-and γ-irradiated samples Hip10 (a, b), Hip8 (c, d) and 61H (e, f), and simulated signals present in those spectra (g).…”

“…At least two more signals are present in the spectra of γ-irradiated samples (Figure 2 b, d, f): a narrow line at g = 2.0034 strongly overlapped by the orthorhombic CO 2 − signal, and a weak line at g = 2.0000. The first one is presumably connected with one of the carbonate species, such as axial CO 3 3with g = 2.0033, g = 2.0013 (Eachus and Symons 1968;Callens 1997;Baїetto et al 1999;Sato and Ikeya 2005;Sadło et al 2015;Kabacińska et al 2019), or alternatively with a SO 3center with an axial (g = 2.0034, g = 2.0019) or isotropic (g = 2.0031) symmetry (Kai and Miki 1992; Ikeya 1993Ikeya , 2004Miki et al 1993;Baїetto et al 1999;Bartoll et al 2000;Kabacińska et al 2019). The signal at g = 2.0000, is described in the literature as a surface defect-electrons trapped at an CO 3 2vacancy created by grinding (Grün 1991;Bahain et al 1994;Bartoll et al 2000;Kabacińska et al 2017Kabacińska et al , 2019.…”