Laboratoire de Chimie Physique/ELYSE, UMR 8000 CNRS/ Université Paris-Sud 11, Orsay, France.
J Phys Chem A. 2012 Nov 29;116(47):11509-18. doi: 10.1021/jp309381z. Epub 2012 Nov 14.
Picosecond pulse-probe radiolysis measurements of highly concentrated Cl(-) aqueous solutions are used to probe the oxidation mechanism of the Cl(-). The transient absorption spectra are measured from 340 to 710 nm in the picosecond range for the ultrafast electron pulse radiolysis of halide solutions at different concentrations up to 8 M. The amount of Cl(2)(•-) formation within the electron pulse increases notably with increasing Cl(-) concentration. Kinetic measurements reveal that the direct ionization of Cl(-) cannot solely explain the significant amount of fast Cl(2)(•-) formation within the electron pulse. The results suggest that Cl(-) reacts with the precursor of the OH(•) radical, i.e., H(2)O(•+) radical, to form Cl(•) atom within the electron pulse and the Cl(•) atom reacts subsequently with Cl(-) to form Cl(2)(•-) on very short time scales. The proton transfer reaction between H(2)O(•+) and the water molecule competes with the electron transfer reaction between Cl(-) and H(2)O(•+). Molecular dynamics simulations show that number of water molecules in close proximity decreases with increasing concentration of the salt (NaCl), confirming that for highly concentrated solutions the proton transfer reaction between H(2)O(•+) and a water molecule becomes less efficient. Diffusion-kinetic simulations of spur reactions including the direct ionization of Cl(-) and hole scavenging by Cl(-) show that up to 30% of the H(2)O(•+) produced by the irradiation could be scavenged for solutions containing 5.5 M Cl(-). This process decreases the yield of OH(•) radical in solution on the picosecond time scale. The experimental results for the same concentration of Cl(-) at a given absorbed dose show that the radiation energy absorbed by counterions is transferred to Cl(-) or water molecules and the effect of the countercation such as Li(+), K(+), Na(+), and Mg(2+) on the oxidation yield of Cl(-) is negligible.
皮秒脉冲探针辐射分解测量高浓度 Cl(-) 水溶液，用于探测 Cl(-) 的氧化机制。在不同浓度高达 8 M 的卤化物溶液的超快电子脉冲辐射分解中，在皮秒范围内测量了从 340 到 710nm 的瞬态吸收光谱。在电子脉冲中 Cl(2)(•-)的形成量随着 Cl(-)浓度的增加而显著增加。动力学测量表明，Cl(-)的直接电离不能单独解释电子脉冲中大量快速 Cl(2)(•-)的形成。结果表明，Cl(-)与 OH(•)自由基的前体即 H(2)O(•+)自由基反应，在电子脉冲中形成 Cl(•)原子，Cl(•)原子随后与 Cl(-)反应，在很短的时间尺度内形成 Cl(2)(•-)。H(2)O(•+)和水分子之间的质子转移反应与 Cl(-)和 H(2)O(•+)之间的电子转移反应竞争。分子动力学模拟表明，随着盐（NaCl）浓度的增加，靠近的水分子数量减少，这证实了对于高浓度溶液，H(2)O(•+)和水分子之间的质子转移反应效率降低。包括 Cl(-)的直接电离和 Cl(-)空穴清除的spur 反应的扩散-动力学模拟表明，在含有 5.5 M Cl(-)的溶液中，辐照产生的 H(2)O(•+)中高达 30%可能被清除。这个过程在皮秒时间尺度上降低了溶液中 OH(•)自由基的产率。在相同浓度的 Cl(-)和给定吸收剂量下的实验结果表明，反离子吸收的辐射能转移到 Cl(-)或水分子中，Li(+)、K(+)、Na(+)和 Mg(2+)等抗衡阳离子对 Cl(-)氧化产率的影响可以忽略不计。
