The Negligible Role of C鈥揌 Stretch Excitation in the Physisorption of CH4 on Pt(111)

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• 作者：Li Chen ; Hirokazu Ueta ; Helen Chadwick ; Rainer D. Beck
• 刊名：Journal of Physical Chemistry C
• 出版年：2015
• 出版时间：July 2, 2015
• 年：2015
• 卷：119
• 期：26
• 页码：14499-14505
• 全文大小：314K
• ISSN：1932-7455

文摘

We report a molecular beam study of the effect of vibrational excitation on the physisorption of methane on a Pt(111) surface. Our experiments use a continuous molecular beam of CH₄, prepared in its antisymmetic C鈥揌 stretch mode 谓₃ by infrared laser pumping via rapid adiabatic passage. Physisorbed CH₄(ads) is detected on a Pt(111) surface by reflection absorption infrared spectroscopy. At a surface temperature of 77 K, the desorption lifetime of CH₄(ads) is observed to be 0.4 卤 0.2 s. Trapping probabilities for the incident CH₄ are measured by the King and Wells beam reflectivity method with and without vibrational excitation. Vibrational excitation of the incident CH₄ with one quantum of 谓₃ vibration does not produce a measurable effect (less than 0.2% change) on the trapping probability, in sharp contrast to the dissociative chemisorption process. The effect of resonant vibrational excitation of physisorbed CH₄(ads) on its dissociation rate was also investigated.