Nanayakkara Charith E, Jayaweera Pradeep M, Rubasinghege Gayan, Baltrusaitis Jonas, Grassian Vicki H
Department of Chemistry, University of Iowa , Iowa City, Iowa 52242, United States.
J Phys Chem A. 2014 Jan 9;118(1):158-66. doi: 10.1021/jp409017m. Epub 2013 Dec 20.
The surface photochemistry of nitrate, formed from nitric acid adsorption, on hematite (α-Fe2O3) particle surfaces under different environmental conditions is investigated using X-ray photoelectron spectroscopy (XPS). Following exposure of α-Fe2O3 particle surfaces to gas-phase nitric acid, a peak in the N1s region is seen at 407.4 eV; this binding energy is indicative of adsorbed nitrate. Upon broadband irradiation with light (λ > 300 nm), the nitrate peak decreases in intensity as a result of a decrease in adsorbed nitrate on the surface. Concomitant with this decrease in the nitrate coverage, there is the appearance of two lower binding energy peaks in the N1s region at 401.7 and 400.3 eV, due to reduced nitrogen species. The formation as well as the stability of these reduced nitrogen species, identified as NO(-) and N(-), are further investigated as a function of water vapor pressure. Additionally, irradiation of adsorbed nitrate on α-Fe2O3 generates three nitrogen gas-phase products including NO2, NO, and N2O. As shown here, different environmental conditions of water vapor pressure and the presence of molecular oxygen greatly influence the relative photoproduct distribution from nitrate surface photochemistry. The atmospheric implications of these results are discussed.
利用X射线光电子能谱（XPS）研究了在不同环境条件下，硝酸吸附在赤铁矿（α-Fe₂O₃）颗粒表面形成的硝酸盐的表面光化学。将α-Fe₂O₃颗粒表面暴露于气相硝酸后，在N1s区域407.4 eV处出现一个峰；该结合能表明存在吸附的硝酸盐。在用宽带光（λ > 300 nm）照射后，由于表面吸附的硝酸盐减少，硝酸盐峰的强度降低。随着硝酸盐覆盖度的降低，由于氮物种的还原，在N1s区域401.7和400.3 eV处出现两个较低结合能的峰。作为水蒸气压力的函数，进一步研究了这些被确定为NO⁻和N⁻的还原氮物种的形成及其稳定性。此外，α-Fe₂O₃上吸附的硝酸盐的照射产生三种气相氮产物，包括NO₂、NO和N₂O。如下所示，水蒸气压力和分子氧的存在等不同环境条件极大地影响了硝酸盐表面光化学的相对光产物分布。讨论了这些结果对大气的影响。
