The temperature dependence of the rate constant () of the bimolecular reaction of two hydrated electrons () measured in alkaline water exhibits an abrupt drop between 150°C and 200°C; above 250°C, it is too small to be measured reliably. Although this result is well established, the applicability of this sudden drop in ) above to neutral or slightly acidic solution, as recommended by some authors, still remains uncertain. In fact, the recent work suggested that in near-neutral water the abrupt change in above does not occur and that should increase, rather than decrease, at temperatures greater than 150°C with roughly the same Arrhenius dependence of the data below 150°C. In view of this uncertainty of , Monte Carlo simulations were used in this study to examine the sensitivity of the density dependence of the yield of in the low–linear energy transfer (LET) radiolysis of supercritical water () at 400°C on variations in the temperature dependence of . Two different values of the self-reaction rate constant at 400°C were used: one was based on the temperature dependence of above 150°C as measured in alkaline water (), and the other was based on an Arrhenius extrapolation of the values below 150°C (). In both cases, the density dependences of our calculated yields at and 1 ns were found to compare fairly well with the available picosecond pulse radiolysis experimental data (for ) for the entire water density range studied (). Only a small effect of on the variation of ) as a function of density at 60 ps and 1 ns could be observed. In conclusion, our present calculations did not allow us to unambiguously confirm (or deny) the applicability of the predicted sudden drop of at in near-neutral water.
Radiolysis of Supercritical Water at 400°C: A Sensitivity Study of the Density Dependence of the Yield of Hydrated Electrons on the (eaq−+eaq−) Reaction Rate Constant
Manuscript received March 28, 2015; final manuscript received July 1, 2015; published online February 29, 2016. Assoc. Editor: Thomas Schulenberg.
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Sanguanmith, S., Meesungnoen, J., Guzonas, D. A., Stuart, C. R., and Jay-Gerin, J. (February 29, 2016). "Radiolysis of Supercritical Water at 400°C: A Sensitivity Study of the Density Dependence of the Yield of Hydrated Electrons on the (eaq−+eaq−) Reaction Rate Constant." ASME. ASME J of Nuclear Rad Sci. April 2016; 2(2): 021014. https://doi.org/10.1115/1.4031013
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