Ultrafast pre-solvated dodecane hole capture and subsequent damage of used nuclear fuel extraction ligands DEHBA, DEH<i>i</i>BA, HONTA, CMPO, HEH[EHP] and TBP

Two classes of used nuclear fuel (UNF) extraction ligands, amide (DEHBA, DEH<i>i</i>BA, HONTA) and organophosphorus (CMPO, HEH[EHP], TBP), were selected to study radiation induced damage at picosecond to nanosecond timescale using electron pulse radiolysis in <i>n</i>-dodecane (DD) and supported by quantum chemical calculations. Spectra after radiolysis of 200 mM extraction ligands were recorded in DD/0.3 M DCM. Absorption peaks at 365, 365, 400 and 387 nm in case of DEHBA, DEH<i>i</i>BA, HONTA and CMPO respectively are assigned to triplet excited states. Additional absorption peaks at 420, 460 and 600 nm of DEHBA, DEH<i>i</i>BA and HONTA respectively were identified as due to ligand radical cations. A concentration dependent absorption peak at 600 nm in the case of CMPO was observed and assigned due to a combination of CMPO˙⁺, (CMPO)₂˙⁺ and possibly a radical degradation product of CMPO. Weak absorption peaks at 650 and 550 nm in case of HEH[EHP] and TBP were observed and tentatively assigned to their radical cations. A two-component DD˙⁺ decay in the presence of ligands was observed due to different ligand oxidation mechanisms: ultrafast capture of pre-solvated DD holes and diffusive capture of solvated DD holes. At high extraction ligand concentrations (>100 mM), the majority of DD holes were captured <i>via</i> the ultrafast pre-solvated pathway in <10 ps with <i>C</i>₃₇ values of 389, 401, 270, 374, 458 and 340 mM for DEHBA, DEH<i>i</i>BA, HONTA, CMPO, HEH[EHP] and TBP respectively. Following ultrafast capture, the remainder of DD holes became solvated and were captured with <i>k</i> = (2.32 ± 0.13), (1.78 ± 0.12), (1.38 ± 0.2), (0.98 ± 0.081), (1.09 ± 0.08) and (1.77 ± 0.046) × 10¹⁰ for DEHBA, DEH<i>i</i>BA, HONTA, CMPO, HEH[EHP] and TBP respectively. Subsequent hole transfer from the extraction ligands˙⁺ to the low IP solute tri-<i>p</i>-tolylamine (TTA) showed only 4-16% hole transfer, most likely indicating ligand˙⁺ degradation in 0.9-4.6 ns.