Ghosal Sutapa, Brown Matthew A, Bluhm Hendrik, Krisch Maria J, Salmeron Miquel, Jungwirth Pavel, Hemminger John C
Physical and Life Sciences Directorate, Lawrence Livermore National Laboratory, L-437, Livermore California 94551, USA.
J Phys Chem A. 2008 Dec 4;112(48):12378-84. doi: 10.1021/jp805490f.
The chemistry of Br species associated with sea salt ice and aerosols has been implicated in the episodes of ozone depletion reported at Arctic sunrise. However, Br(-) is only a minor component in sea salt, which has a Br(-)/Cl(-) molar ratio of approximately 0.0015. Sea salt is a complex mixture of many different species, with NaCl as the primary component. In recent years experimental and theoretical studies have reported enhancement of the large, more polarizable halide ion at the liquid/vapor interface of corresponding aqueous alkali halide solutions. The proposed enhancement is likely to influence the availability of sea salt Br(-) for heterogeneous reactions such as those involved in the ozone depletion episodes. We report here ambient pressure X-ray photoelectron spectroscopy studies and molecular dynamics simulations showing direct evidence of Br(-) enhancement at the interface of an aqueous NaCl solution doped with bromide. The experiments were carried out on samples with Br(-)/Cl(-) ratios in the range 0.1% to 10%, the latter being also the ratio for which simulations were carried out. This is the first direct measurement of interfacial enhancement of Br(-) in a multicomponent solution with particular relevance to sea salt chemistry.
与海盐冰和气溶胶相关的溴物种的化学过程，被认为与北极日出时报道的臭氧消耗事件有关。然而，溴离子（Br⁻）在海盐中只是次要成分，其溴离子/氯离子（Br⁻/Cl⁻）摩尔比约为0.0015。海盐是许多不同物种的复杂混合物，氯化钠（NaCl）是主要成分。近年来，实验和理论研究报道了在相应碱金属卤化物水溶液的液/气界面处，较大的、极化率更高的卤离子有所增加。这种增加可能会影响海盐中溴离子（Br⁻）参与非均相反应（如那些与臭氧消耗事件有关的反应）的可用性。我们在此报告常压X射线光电子能谱研究和分子动力学模拟，其显示了在掺杂溴化物的氯化钠水溶液界面处溴离子（Br⁻）增加的直接证据。实验是在溴离子/氯离子（Br⁻/Cl⁻）比率在0.1%至10%范围内的样品上进行的，后者也是进行模拟的比率。这是首次在与海盐化学特别相关的多组分溶液中直接测量溴离子（Br⁻）的界面增加情况。
