Nissenson Paul, Knox Christopher J H, Finlayson-Pitts Barbara J, Phillips Leon F, Dabdub Donald
Department of Mechanical and Aerospace Engineering, University of California, Irvine, California 92697-3975, USA.
Phys Chem Chem Phys. 2006 Oct 28;8(40):4700-10. doi: 10.1039/b609219e. Epub 2006 Sep 14.
While there is increasing evidence for unique chemical reactions at interfaces, there are fewer data on photochemistry at liquid-vapor junctions. This paper reports a comparison of the photolysis of molybdenum hexacarbonyl, Mo(CO)(6), in 1-decene either as liquid droplets or in bulk-liquid solutions. Mo(CO)(6) photolysis is faster by at least three orders of magnitude in the aerosols than in bulk-liquids. Two possible sources of this enhancement are considered: (1) increased light intensity due to either Morphology-Dependent Resonances (MDRs) in the spherical aerosol particles and/or to increased pathlengths for light inside the droplet due to refraction, which are termed physical effects in this paper; and (2) interface effects such as an incomplete solvent-cage at the gas-liquid boundary and/or enhanced interfacial concentrations of Mo(CO)(6), which are termed chemical effects. Quantitative calculations of the first possibility were carried out in which the light intensity distribution in the droplets averaged over 215-360 nm was obtained for 1-decene droplets. Calculations show that the average increase in light intensity over the entire droplet is 106%, with an average increase of 51% at the interface. These increases are much smaller than the observed increase in the apparent photolysis rate of droplets compared to the bulk. Thus, chemical effects, i.e., a decreased solvent-cage effect at the interface and/or enhancement in the surface concentration of Mo(CO)(6), are most likely responsible for the dramatic increase in the photolysis rate. Similar calculations were also carried out for broadband (290-600 nm) solar irradiation of water droplets, relevant to atmospheric conditions. These calculations show that, in agreement with previous calculations by Mayer and Madronich [B. Mayer and S. Madronich, Atmos. Chem. Phys., 2004, 4, 2241] MDRs produce only a moderate average intensity enhancement relative to the corresponding bulk-liquid slabs when averaged over a range of wavelengths characteristic of solar radiation at the Earth's surface. However, as in the case of Mo(CO)(6) in 1-decene, chemical effects may play a role in enhanced photochemistry at the aerosol-air interface for airborne particles.
虽然有越来越多的证据表明界面处存在独特的化学反应，但关于液-气界面光化学的数据却较少。本文报道了六羰基钼（Mo(CO)₆）在1-癸烯中以液滴形式或本体溶液形式光解的比较。与本体液体相比，Mo(CO)₆在气溶胶中的光解速度至少快三个数量级。考虑了这种增强的两个可能来源：（1）由于球形气溶胶颗粒中的形态依赖共振（MDRs）和/或由于折射导致液滴内光程增加而使光强度增加，本文将其称为物理效应；（2）界面效应，如气-液边界处不完全的溶剂笼和/或Mo(CO)₆界面浓度的增加，本文将其称为化学效应。对第一种可能性进行了定量计算，其中获得了1-癸烯液滴在215 - 360 nm范围内平均的液滴内光强度分布。计算表明，整个液滴内光强度的平均增加为106%，界面处平均增加51%。这些增加远小于与本体相比观察到的液滴表观光解速率的增加。因此，化学效应，即在界面处溶剂笼效应的降低和/或Mo(CO)₆表面浓度的增加，最有可能是光解速率急剧增加的原因。还对与大气条件相关的水滴的宽带（290 - 例如，当在地球表面太阳辐射的一系列特征波长上进行平均时，MDRs相对于相应的本体液体平板仅产生适度的平均强度增强。然而，与1-癸烯中Mo(CO)₆的情况一样，化学效应可能在气溶胶-空气界面处增强的光化学中对空气中的颗粒起作用。 600 nm）太阳辐射进行了类似计算。这些计算表明，与Mayer和Madronich先前的计算结果一致[B. Mayer和S. Madronich，Atmos. Chem. Phys.，2004，4，2241]
