Characterization of the 4-oxo-2,2,6,6-tetramethylpiperidinooxy dosimeter for in situ radiolysis electron spin resonance studies.

The stable free radical 4-oxo-2,2,6,6-tetramethylpiperidinooxy (2,2,6,6-tetramethylpiperidone-N-oxyl, TEMPONE) in nitrous oxide-saturated aqueous formate solution has been shown to be a quantitative dosimeter for in situ radiolysis electron spin resonance (ESR) studies. The bleach of the TEMPONE ESR signal is proportional to the absorbed dose in steady-state radiolysis/field-modulation and in pulse radiolysis/time-resolved studies. The G value for consumption of TEMPONE in nitrogen-deoxygenated solution is 5.3 (molecules per 100 eV), while the value in nitrous oxide-saturated solution is 6.0. Measurement of the radiolytically produced yield of carbon dioxide shows that the product of reaction of carbon dioxide radical anion with TEMPONE gives the corresponding hydroxylamine. The stability of the integrated intensity of the TEMPONE ESR bleach has been evaluated in the presence and absence of oxygen and found to be stable for hours. The ESR linewidth of TEMPONE solutions irradiated under anoxic conditions was constant in the postirradiation period. However, when oxygen was added postirradiation, the oxygen-broadened ESR linewidth decreased slowly toward the width observed in anoxic media, indicating consumption of dioxygen by, with concomitant production of, diamagnetic species in solution.