The formation and decay of <tex-math>${\rm HO}_{2}/{\rm O}{}_{2}{}^{-}$</tex-math> radical from the radiolysis of water by heavy <tex-math>${}^{36}{\rm S}{}^{16+}$</tex-math> ions (2.7 GeV) have been observed by time-resolved absorption spectroscopy at 260 nm. The experiment was performed at the Grand Accélérateur National d'Ions Lourds (Caen, France). In deaerated water, for a linear energy transfer (LET) of 250 eV/nm, the yield of <tex-math>${\rm HO}_{2}/{\rm O}{}_{2}{}^{-}$</tex-math> is (6 ± 2) × <tex-math>$10^{-9}\ {\rm mol}\ {\rm J}^{-1}$</tex-math>. In aerated solution, an additional formation of O2- is observed due to the reaction of hydrogen atom and <tex-math>${\rm e}{}_{{\rm aq}}{}^{-}$</tex-math> with oxygen. The experimental G values are compared to those obtained with light ions for the same LET. The importance of the initial velocity is discussed briefly.

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