Doronin M, Bertin M, Michaut X, Philippe L, Fillion J-H
LERMA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, UPMC Univ. Paris 06, F-75252 Paris, France.
J Chem Phys. 2015 Aug 28;143(8):084703. doi: 10.1063/1.4929376.
In this paper, we have studied adsorption and thermal desorption of methanol CH3OH on graphite surface, with the specific aim to derive from experimental data quantitative parameters that govern the desorption, namely, adsorption energy Eads and prefactor ν of the Polanyi-Wigner law. In low coverage regime, these two values are interconnected and usually the experiments can be reproduced with any couple (Eads, ν), which makes intercomparison between studies difficult since the results depend on the extraction method. Here, we use a method for determining independently the average adsorption energy and a prefactor value that works over a large range of incident methanol coverage, from a limited set of desorption curves performed at different heating rates. In the low coverage regime the procedure is based on a first order kinetic law, and considers an adsorption energy distribution which is not expected to vary with the applied heating rate. In the case of CH3OH multilayers, Eads is determined as 430 meV with a prefactor of 5 × 10(14) s(-1). For CH3OH submonolayers on graphite, adsorption energy of 470 ± 30 meV and a prefactor of (8 ± 3) × 10(16) s(-1) have been found. These last values, which do not change between 0.09 ML and 1 ML initial coverage, suggest that the methanol molecules form island-like structure on the graphite even at low coverage.
在本文中，我们研究了甲醇（CH₃OH）在石墨表面的吸附和热脱附，具体目的是从实验数据中推导出控制脱附的定量参数，即吸附能Eads和玻尔兹曼-维格纳定律的前因子ν。在低覆盖度区域，这两个值相互关联，通常任何一对（Eads，ν）都能重现实验结果，这使得不同研究之间的相互比较变得困难，因为结果取决于提取方法。在这里，我们使用一种方法，通过在不同加热速率下进行的有限数量的脱附曲线，独立确定平均吸附能和在前因子值，该方法适用于大范围的入射甲醇覆盖度。在低覆盖度区域，该程序基于一级动力学定律，并考虑了预期不会随所施加加热速率变化的吸附能分布。对于甲醇多层膜，确定Eads为430毫电子伏，前因子为5×10¹⁴ s⁻¹。对于石墨上的甲醇亚单层，发现吸附能为470±30毫电子伏，前因子为(8±3)×10¹⁶ s⁻¹。这些最后的值在初始覆盖度从0.09单层到1单层之间没有变化，这表明即使在低覆盖度下，甲醇分子在石墨上也形成岛状结构。
