Interaction of Acetonitrile with Alcohols at Cryogenic Temperatures

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• 作者：Rabin Rajan J. Methikkalam ; Radha Gobinda Bhuin ; Jyotirmoy Ghosh ; Bhalamurugan Sivaraman ; Thalappil Pradeep
• 刊名：Journal of Physical Chemistry C
• 出版年：2017
• 出版时间：February 9, 2017
• 年：2017
• 卷：121
• 期：5
• 页码：2822-2835
• 全文大小：1038K
• ISSN：1932-7455

文摘

Temperature-dependent interaction of acetonitrile with methanol and ethanol, as codeposited and sequentially deposited films, was studied in the 10–130 K window, in ultra high vacuum. Films in the range of 50–100 monolayers were investigated using temperature-dependent reflection–absorption infrared spectroscopy (RAIRS), Cs⁺ ion scattering mass spectrometry, and temperature-programmed desorption (TPD). Acetonitrile interacts with methanol and ethanol through intermolecular hydrogen bonding. When a codeposited system was annealed, acetonitrile underwent a phase segregation at 110 K, and large changes in the infrared spectrum were observed. The OH stretching of methanol gave two peaks characteristic of the change to the α-phase of methanol, while ethanol gave three peaks at the same temperature. The surface composition of the systems probed by 40 eV Cs⁺ scattering showed that both the alcohols and the acetonitrile were of equal intensity below 110 K, while above 110 K the intensity of the latter went down substantially. We find that the presence of acetonitrile does not allow ethanol to undergo complete phase transition prior to desorption, while methanol could do so. This behavior is explained on the basis of the size, extent of hydrogen bonding, and phase transition temperature, of the two alcohols. Additional peaks in the hydroxyl region observed in alcohols in the 110–130 K window may be used as a signature of the presence of acetonitrile mixed with alcohol, especially ethanol, and hence this may be used in observational studies of such molecular environments.