Adsorption and Hydrolysis of Alcohols and Carbonyls on Ice at Temperatures of the Upper Troposphere

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• 作者：Angela Symington ; Lay May Leow ; Paul T. Griffiths ; R. Anthony Cox
• 刊名：The Journal of Physical Chemistry A
• 出版年：2012
• 出版时间：June 21, 2012
• 年：2012
• 卷：116
• 期：24
• 页码：5990-6002
• 全文大小：601K
• 年卷期：v.116,no.24(June 21, 2012)
• ISSN：1520-5215

文摘

The uptake of gaseous ethanol, 1,1,1-trifluoroethanol, acetone, chloral (CClub>3ub>CHO), and fluoral (CFub>3ub>CHO) on ice films has been investigated using a coated-wall flow tube at temperatures 208鈥?28 K corresponding to the upper troposphere (UT), with a mass spectrometric measurement of gas concentration. The uptake was largely reversible and followed Langmuir-type kinetic behavior, i.e., surface coverage increased with the trace gas concentration approaching a maximum surface coverage at a gas phase concentration of Nub>maxub> (2鈥?) 脳 10up>14up> molecules cmup>鈥?up>, corresponding to a surface coverage of 30% of a monolayer (ML). The equilibrium partition coefficients, Kub>LinCub>, were obtained from the experimental data by analysis using the simple Langmuir model for specific conditions of temperature and concentration. The analysis showed that the Kub>LinCub> depend only weakly on surface coverages. The following expressions described the temperature dependence of the partition coefficients (Kub>LinCub>) in centimeters, at low coverage for ethanol, trifluoroethanol, acetone, chloral, and fluoral: Kub>LinCub> = 1.36 脳 10up>鈥?1up>鈥塭xp(5573.5/T), Kub>LinCub> = 3.74 脳 10up>鈥?2up>鈥塭xp(6427/T), Kub>LinCub> = 3.04 脳 10up>鈥?up>鈥塭xp(4625/T), Kub>LinCub> = 7.52 脳 10up>鈥?up>鈥塭xp(2069/T), and Kub>LinCub> = 1.06 脳 10up>鈥?up>鈥塭xp(904/T). For acetone and ethanol the enthalpies and entropies of adsorption derived from all available data showed systematic temperature dependence, which is attributed to temperature dependent surface modifications, e.g., QLL formation. For chloral and fluoral, there was an irreversible component of uptake, which was attributed to hydrate formation on the surface. Rate constants for these surface reactions derived using a Langmuir鈥揌inshelwood mechanism are reported.