Wadsworth Center, New York State Department of Health and Department of Environmental Health Sciences, State University of New York , Albany, New York 12201-0509, United States.
J Phys Chem A. 2013 Sep 12;117(36):8907-14. doi: 10.1021/jp405573y. Epub 2013 Aug 27.
We have determined absorption cross sections of a monolayer of H2O adsorbed on the fused silica surfaces in the 295-370 nm region at 293 ± 1 K by using Brewster angle cavity ring-down spectroscopy. Absorption cross sections of surface-adsorbed H2O vary between (4.66 ± 0.83) × 10(-20) and (1.73 ± 0.52) × 10(-21) cm(2)/molecule over this wavelength range, where errors quoted represent experimental scatter (1σ). Our experimental study provides direct evidence that surface-adsorbed H2O is an absorber of the near UV solar radiation. We also varied the H2O pressure in the surface study cell over the 0.01-17 Torr range and obtained probe laser absorptions at 295, 340, and 350 nm by multilayer of adsorbed H2O molecules until the heterogeneous nucleation of water occurred on fused silica surfaces. The average absorption cross sections of multilayer adsorbed H2O are (2.17 ± 0.53) × 10(-20), (2.48 ± 0.67) × 10(-21), and (2.34 ± 0.59) × 10(-21) cm(2)/molecule at 295, 340, and 350 nm. The average absorption cross sections of transitional H2O layer are (6.06 ± 2.73) × 10(-20), (6.48 ± 3.85) × 10(-21), and (8.04 ± 4.92) × 10(-21) cm(2)/molecule at 295, 340, and 350 nm. The average thin water film absorption cross sections are (2.39 ± 0.50) × 10(-19), (3.21 ± 0.81) × 10(-20), and (3.37 ± 0.94) × 10(-20) cm(2)/molecule at 295 nm, 340 nm, and 350 nm. Atmospheric implications of the results are discussed.
我们使用布鲁斯特角腔衰荡光谱法在 293±1 K 下测定了 295-370nm 区域内吸附在熔融石英表面的单层 H2O 的吸收截面。在这个波长范围内，表面吸附的 H2O 的吸收截面在(4.66±0.83)×10(-20)和(1.73±0.52)×10(-21)cm(2)/分子之间变化，这里给出的误差表示实验分散度(1σ)。我们的实验研究提供了直接证据，证明表面吸附的 H2O 是近紫外太阳辐射的吸收体。我们还在表面研究单元中改变了 H2O 压力，范围在 0.01-17 托，并通过多层吸附的 H2O 分子获得了 295、340 和 350nm 处的探测激光吸收，直到水在熔融石英表面上发生非均相成核。多层吸附的 H2O 的平均吸收截面在 295、340 和 350nm 处分别为(2.17±0.53)×10(-20)、(2.48±0.67)×10(-21)和(2.34±0.59)×10(-21)cm(2)/分子。过渡 H2O 层的平均吸收截面在 295、340 和 350nm 处分别为(6.06±2.73)×10(-20)、(6.48±3.85)×10(-21)和(8.04±4.92)×10(-21)cm(2)/分子。薄水膜的平均吸收截面在 295nm、340nm 和 350nm 处分别为(2.39±0.50)×10(-19)、(3.21±0.81)×10(-20)和(3.37±0.94)×10(-20)cm(2)/分子。讨论了结果的大气影响。
