Self-Organization of 1-Methylnaphthalene on the Surface of Artificial Snow Grains: A Combined Experimental鈥揅omputational Approach

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• 作者：Dominik Heger ; Dana Nachtigallov谩 ; Franti拧ek Surman ; J谩n Krausko ; Beata Magyarov谩 ; Miroslav Brumovsk媒 ; Miroslav Rube拧 ; Ivan Gladich ; Petr Kl谩n
• 刊名：Journal of Physical Chemistry A
• 出版年：2011
• 出版时间：October 20, 2011
• 年：2011
• 卷：115
• 期：41
• 页码：11412-11422
• 全文大小：1044K
• 年卷期：v.115,no.41(October 20, 2011)
• ISSN：1520-5215

文摘

A combined experimental鈥揷omputational approach was used to study the self-organization and microenvironment of 1-methylnaphthalene (1MN) deposited on the surface of artificial snow grains from vapors at 238 K. The specific surface area of this snow (1.1 脳 10⁴ cm² g^鈥?), produced by spraying very fine droplets of pure water from a nebulizer into liquid nitrogen, was determined using valerophenone photochemistry to estimate the surface coverage by 1MN. Fluorescence spectroscopy at 77 K, in combination with molecular dynamics simulations, and density functional theory (DFT) and second-order coupled cluster (CC2) calculations, provided evidence for the occurrence of ground- and excited-state complexes (excimers) and other associates of 1MN on the snow grains鈥?surface. Only weak excimer fluorescence was observed for a loading of 5 脳 10^鈥? mol kg^鈥?, which is 2鈥? orders of magnitude below monolayer coverage. However, the results indicate that the formation of excimers is favored at higher surface loadings (>5 脳 10^鈥? mol kg^鈥?), albeit still being below monolayer coverage. The calculations of excited states of monomer and associated moieties suggested that a parallel-displaced arrangement is responsible for the excimer emission observed experimentally, although some other associations, such as T-shape dimer structures, which do not provide excimer emission, can still be relatively abundant at this surface concentration. The hydrophobic 1MN molecules, deposited on the ice surface, which is covered by a relatively flexible quasi-liquid layer at 238 K, are then assumed to be capable of dynamic motion resulting in the formation of energetically preferred associations to some extent. The environmental implications of organic compounds鈥?deposition on snow grains and ice are discussed.