Competition Reactions of H2O鈥? Radical in Concentrated Cl鈥?/sup> Aqueous Solutions: Picosecond Pulse Radiolysis Study
详细信息 查看全文
- 作者：Abdel Karim El Omar ; Uli Schmidhammer ; Bernard Rousseau ; Jay LaVerne ; Mehran Mostafavi
- 刊名：The Journal of Physical Chemistry A
- 出版年：2012
- 出版时间：November 29, 2012
- 年：2012
- 卷：116
- 期：47
- 页码：11509-11518
- 全文大小：499K
- 年卷期：v.116,no.47(November 29, 2012)
- ISSN：1520-5215
文摘
Picosecond pulse鈥損robe radiolysis measurements of highly concentrated Cl鈥?/sup> aqueous solutions are used to probe the oxidation mechanism of the Cl鈥?/sup>. 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 Cl2鈥⑩€?/sup> formation within the electron pulse increases notably with increasing Cl鈥?/sup> concentration. Kinetic measurements reveal that the direct ionization of Cl鈥?/sup> cannot solely explain the significant amount of fast Cl2鈥⑩€?/sup> formation within the electron pulse. The results suggest that Cl鈥?/sup> reacts with the precursor of the OH鈥?/sup> radical, i.e., H2O鈥? radical, to form Cl鈥?/sup> atom within the electron pulse and the Cl鈥?/sup> atom reacts subsequently with Cl鈥?/sup> to form Cl2鈥⑩€?/sup> on very short time scales. The proton transfer reaction between H2O鈥? and the water molecule competes with the electron transfer reaction between Cl鈥?/sup> and H2O鈥?. 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 H2O鈥? and a water molecule becomes less efficient. Diffusion-kinetic simulations of spur reactions including the direct ionization of Cl鈥?/sup> and hole scavenging by Cl鈥?/sup> show that up to 30% of the H2O鈥? produced by the irradiation could be scavenged for solutions containing 5.5 M Cl鈥?/sup>. This process decreases the yield of OH鈥?/sup> radical in solution on the picosecond time scale. The experimental results for the same concentration of Cl鈥?/sup> at a given absorbed dose show that the radiation energy absorbed by counterions is transferred to Cl鈥?/sup> or water molecules and the effect of the countercation such as Li+, K+, Na+, and Mg2+ on the oxidation yield of Cl鈥?/sup> is negligible.