Diffusion and Crystallization of Dichloromethane within the Pores of Amorphous Solid Water

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• 作者：Radha Gobinda Bhuin ; Rabin Rajan J. Methikkalam ; Soumabha Bag ; Thalappil Pradeep
• 刊名：Journal of Physical Chemistry C
• 出版年：2016
• 出版时间：June 30, 2016
• 年：2016
• 卷：120
• 期：25
• 页码：13474-13484
• 全文大小：687K
• 年卷期：0
• ISSN：1932-7455

文摘

Dichloromethane (CH₂Cl₂) thin films deposited on Ru(0001) at low temperatures (∼80 K or lower) undergo a phase transition at ∼95 K, manifested by the splitting of its wagging mode at 1265 cm^–1, due to factor group splitting. This splitting occurs at relatively higher temperatures (∼100 K) when amorphous solid water (ASW) is deposited over it, with a significant reduction in intensity of the high-wavenumber component (of the split peaks). Control experiments showed that the intensity of the higher wavenumber peak is dependent on the thickness of the water overlayer. It is proposed that diffusion of CH₂Cl₂ into ASW occurs and it crystallizes within the pores of ASW, which increases the transition temperature. However, the dimensions of the CH₂Cl₂ crystallites get smaller with increasing thickness of ASW with concomitant change in the intensity of the factor group split peak. Control experiments support this suggestion. We propose that the peak intensities can be correlated with the porosity of the ice film. Diffusion of CH₂Cl₂ has been supported by low-energy Cs⁺ scattering and temperature-programmed desorption spectroscopies.