Spectroscopic Properties of Benzene at the Air鈥揑ce Interface: A Combined Experimental鈥揅omputational Approach

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• 作者：Rafa艂 Kania ; Joseph K鈥橢kuboni Malongwe ; Dana Nachtigallov谩 ; J谩n Krausko ; Ivan Gladich ; Martina Roeselov谩 ; Dominik Heger ; Petr Kl谩n
• 刊名：Journal of Physical Chemistry A
• 出版年：2014
• 出版时间：September 4, 2014
• 年：2014
• 卷：118
• 期：35
• 页码：7535-7547
• 全文大小：445K
• ISSN：1520-5215

文摘

A combined experimental and computational approach was used to study the spectroscopic properties of benzene at the ice鈥揳ir interface at 253 and 77 K in comparison with its spectroscopic behavior in aqueous solutions. Benzene-contaminated ice samples were prepared either by shock-freezing of benzene aqueous solutions or by benzene vapor-deposition on pure ice grains and examined using UV diffuse reflectance and emission spectroscopies. Neither the absorption nor excitation nor emission spectra provided unambiguous evidence of benzene associates on the ice surface even at a higher surface coverage. Only a small increase in the fluorescence intensity in the region above 290 nm found experimentally might be associated with formation of benzene excimers perturbed by the interaction with the ice surface as shown by ADC(2) excited-state calculations. The benzene associates were found by MD simulations and ground-state DFT calculations, although not in the arrangement that corresponds to the excimer structures. Our experimental results clearly demonstrated that the energy of the S₀ 鈫?S₁ electronic transition of benzene is not markedly affected by the phase change or the microenvironment at the ice鈥揳ir interface and its absorption is limited to the wavelengths below 268 nm. Neither benzene interactions with the water molecules of ice nor the formation of dimers and microcrystals at the air鈥搃ce interface thus causes any substantial bathochromic shift in its absorption spectrum. Such a critical evaluation of the photophysical properties of organic contaminants of snow and ice is essential for predictions and modeling of chemical processes occurring in polar regions.