Behavior of Heptavalent Technetium in Sulfuric Acid under α‑Irradiation: Structural Determination of Technetium Sulfate Complexes by X‑ray Absorption Spectroscopy and First Principles Calculations

The effect of α-radiolysis on the behavior of heptavalent technetium has been investigated in 13 and 18 M H₂SO₄. Irradiation experiments were performed using α-particles (⁴He²⁺, <i>E</i> = 68 MeV) generated by the ARRONAX cyclotron. UV–visible and X-ray absorption fine structure spectroscopic studies indicate that Tc­(VII) is reduced to Tc­(V) under α-irradiation. Extended X-ray absorption fine structure (EXAFS) spectroscopy measurements are consistent with the presence of mononuclear technetium sulfate complexes. Experimental results and density functional calculations show the formation of [TcO­(HSO₄)₃(H₂O)­(OH)]⁻ and/or [TcO­(HSO₄)₃(H₂O)₂] and [Tc­(HSO₄)₃(SO₄)­(H₂O)] and/or [Tc­(HSO₄)₃(SO₄)­(OH)]⁻ for 13 and 18 M H₂SO₄, respectively