AVS 51st International Symposium
    Surface Science Tuesday Sessions
       Session SS1-TuA

Paper SS1-TuA8
Characterization of Ethylidene and Methylidyne on Pt(111) with Infrared Spectroscopy

Tuesday, November 16, 2004, 3:40 pm, Room 210B

Session: Hydrocarbon Reactions on Metal Surfaces
Presenter: R. Deng, University of Illinois at Chicago
Authors: R. Deng, University of Illinois at Chicago
E. Herceg, University of Illinois at Chicago
M. Trenary, University of Illinois at Chicago
Correspondent: Click to Email
Hydrocarbon intermediates formed in the adsorption and decomposition of ethylene (C@sub 2@H@sub 4@), diiodomethane (CH@sub 2@I@sub 2@) and iodomethane (CH@sub 3@I) on Pt(111) were investigated using reflection absorption infrared spectroscopy (RAIRS) and mass spectrometry. The ethylidene (CHCH@sub 3@) species is identified on the basis of RAIRS peaks at 2960 cm@super -1@ and 1387 cm@super -1@ that are assigned to the CH@sub 3@ asymmetric stretch and the CH@sub 3@ symmetric bend, respectively. It is found that the highest ethylidene coverage can be produced by ethylene exposure to the surface at temperatures around 280 K. Ethylidene undergoes rapid hydrogenation upon exposure to 2x10@super -7@ Torr of H@sub 2@ at 250 K to produce gas phase ethane, as detected by a mass spectrometer. The results indicate that ethylidene could be an intermediate in ethylene hydrogenation on transition metal surfaces near room temperature. Surface methylidyne can be formed in multiple ways: thermal decomposition of diiodomethane and iodomethane; ethylene decomposition at a temperature of about 500 K; and surface carbon hydrogenation. Methylidyne is identified by a CH (CD) stretch mode at 2956 (2206) cm@super -1@. The co-adsorption of surface hydrogen and iodine causes this band to shift to higher frequency. The observation of methylidyne at 500 K indicates that C-C bond scission of the initially adsorbed ethylene occurs at this temperature.