Lithium formate for EPR dosimetry: radiation-induced radical trapping at low temperatures.
Radiation-induced primary radicals in lithium formate. A material used in EPR dosimetry have been studied using electron paramagnetic resonance (EPR), electron nuclear double resonance (ENDOR) and ENDOR-Induced EPR (EIE) techniques. In this study, single crystals were X irradiated at 6-8 K and radical formation at these and higher temperatures were investigated. Periodic density functional theory calculations were used to assist in assigning the radical structures. Mainly two radicals are present at 6 K, the well-known CO2(•-) radical and a protonated electron-gain product. Hyperfine coupling tensors for proton and lithium interactions were obtained for these two radicals and show that the latter radical exists in four conformations with various degrees of bending at the radical center. Pairs of CO2(•-) radicals were also observed and the tensor for the electron-electron dipolar coupling was determined for the strongest coupled pair, which exhibited the largest spectral intensity. Upon warming, both the radical pairs and the reduction product decay, the latter apparently by a transient species. Above 200 K the EPR spectrum was mainly due to the CO2(•-) (mono) radicals, which were previously characterized as the dominant species present at room temperature and which account for the dosimetric EPR signal.
a  Department of Physics, University of Oslo, N-0316 Oslo, Norway;
André
A
Krivokapić
Siv G
SG
Aalbergsjø
Hendrik
H
De Cooman
Eli Olaug
EO
Hole
William H
WH
Nelson
Einar
E
Sagstuen
D002245:Carbon Dioxide / Q000737:chemistry*; D003080:Cold Temperature; D004578:Electron Spin Resonance Spectroscopy; D005557:Formaldehyde / Q000737:chemistry*; D005561:Formates / Q000528:radiation effects*; D005609:Free Radicals / Q000737:chemistry*; D006860:Hydrogen Bonding; D008956:Models, Chemical; D008968:Molecular Conformation; D015394:Molecular Structure; D011874:Radiometry / Q000379:methods*; D055672:Static Electricity
D005561:Formates; D005609:Free Radicals; C030544:formic acid; D002245:Carbon Dioxide; C041069:carboxyl radical; D005557:Formaldehyde