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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Radiolysis of Liquid Water at Temperatures up to 300 deg C: A Monte Carlo Simulation Study
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Radiolysis of Liquid Water at Temperatures up to 300 deg C: A Monte Carlo Simulation Study

机译：高达300摄氏度的高温下液态水的辐射分解：蒙特卡洛模拟研究

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Monte Carlo simulations were performed to calculate the temperature dependence of the primary yields (g-values) of the radical and molecular products of the radiolysis of pure, deaerated liquid water by low linear-energy-transfer (LET) radiation. The early energy deposition was approximated by considering short segments (—400 um) of 300-MeV proton tracks (corresponding to an average LET of —0.3 keV/Mm). The subsequent nonhomogeneous chemical evolution of the reactive species formed in these tracks was simulated by using the independent reaction times approximation, which has previously been used successfully to model the radiolysis of liquid water at ambient temperature under various conditions. Our calculated g-values for the radiolytic species: e,, OH, H, H2, and H202, are presented as a function of temperature over the range 25—300 0C. They show an increase in g(e~), g(OH), and [g(H) + g(H2)] and a decrease in g(H202) with increasing temperature, in agreement with existing experimental data. The sensitivity of the results to the values of reaction rate constants and to the temperature dependence of electron thermalization distances (r,,~) was also investigated. It was found that the best agreement with experiment occurs when the distances of electron thermalization decrease with increasing temperature, a result that is at variance with the predictions of previous modeling studies. Such a decrease in ~ as the temperature increases could be linked to an increase in the scattering cross sections of subexcitation electrons that would account for the corresponding decrease in the degree of structural order of water molecules. Our simulations also suggest that the variations of the g-values with temperature, and especially that of g(H2), are better described if we account for the screening of the Coulomb forces between the two e~ in the bimolecular self-reaction of the hydrated electron. Finally, the time-dependent yields of e~, and OH are presented as functions of temperature, in the range l0-I2~l06 s. It was found that the temporal variation of g(e~,) at elevated temperatures is sensitive to the temperature dependence of rib, suggesting that measurements of the decay of hydrated electrons as functions of time and temperature could, in turn, provide information on the thermalization of subexcitation electrons. The good overall accord of our calculated results with the experimental data available from the literature demonstrates that Monte Carlo simulation methods offer a most promising avenue at present to further develop our understanding of temperature effects in the radiolysis of liquid water.
机译：进行了蒙特卡洛模拟，以计算通过低线性能量转移（LET）辐射对纯净脱气液态水进行放射分解所产生的自由基和分子产物的一次产率（g值）与温度的关系。通过考虑300 MeV质子迹线的短片段（-400 um）（相当于平均LET为-0.3 keV / Mm）来估算早期的能量沉积。通过使用独立的反应时间近似，模拟了在这些径迹中形成的反应性物质随后的非均质化学演化，该反应时间近似以前已成功用于模拟环境温度下各种条件下液态水的放射分解。我们计算出的辐射分解物质：e，OH，H，H2和H2O2的g值是温度在25-300 0C范围内的函数。与现有实验数据一致，它们显示出g（e〜），g（OH）和[g（H）+ g（H2）]随温度升高而增加，而g（H2O2）随着温度升高而降低。还研究了结果对反应速率常数值和电子热化距离（r ,,〜）的温度依赖性的敏感性。研究发现，当电子热化距离随温度升高而减小时，与实验的最佳吻合发生，这一结果与以前的建模研究的预测不一致。随着温度的升高，这种降低可与子激发电子的散射截面的增加有关，这将解释水分子的结构序度的相应降低。我们的模拟还表明，如果我们考虑在分子的双分子自反应中两个电子之间的库仑力的筛选，则可以更好地描述g值随温度的变化，尤其是g（H2）的变化。水合电子。最后，e〜和OH随时间的变化率随温度变化而变化，范围为10-I2〜106s。发现在高温下，g（e〜，）的时间变化对肋的温度依赖性很敏感，这表明水合电子衰变随时间和温度的变化的测量反过来可以提供有关温度的信息。次激发电子的热化。我们的计算结果与可从文献中获得的实验数据的良好总体吻合表明，蒙特卡罗模拟方法为当前进一步发展我们对液态水辐射分解中温度效应的理解提供了最有希望的途径。

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