AVS 49th International Symposium
    Surface Science Tuesday Sessions
       Session SS1-TuM

Paper SS1-TuM3
Electron-Induced Dissociation and Reactions of Methyl Groups Adsorbed on Cu(110)

Tuesday, November 5, 2002, 9:00 am, Room C-108

Session: Hydrocarbon Catalysis
Presenter: T.J. Chuang, National Taiwan University, Republic of China
Authors: Y.L. Chan, National Taiwan University, Republic of China
P. Chuang, National Taiwan University, Republic of China
R. Klauser, Synchrotron Radiation Research Center, Taiwan, Republic of China
S.-H. Chien, National Taiwan University, Republic of China
T.J. Chuang, National Taiwan University, Republic of China
Correspondent: Click to Email
Methylene was suggested in some prior studies to be the key species responsible for the propagation of long chain hydrocarbons from methyl groups on catalyst surfaces. So far, direct evidence to show the presence of such reaction intermediate remains elusive, particularly under UHV condition. With the combination of HREELS vibrational spectroscopy, TPD and LEED techniques, we have observed that CH@sub 3@(ads) groups adsorbed on Cu(110) can be dissociated by low energy electrons to form CH@sub 2@(ads). In subsequent thermal process, CH@sub 2@(ads) can react with coadsorbed CH@sub 3@(ads) to produce C@sub 2@H@sub 4@, C@sub 3@H@sub 6@ and C@sub 4@H@sub 8@ molecules desorbed from surface. The desorption peaks for the various alkenes center at the same temperature independent of the CH@sub 2@(ads) average surface concentration and exhibiting the first-order reaction kinetics. Furthermore, the product ratio of C@sub 3@H@sub 6@/C@sub 2@H@sub 4@ is found to be linearly proportional to the ratio of CH@sub 2@(ads)/CH@sub 3@(ads) concentrations. The results show that aggregation of the adsorbates and close proximity of the reactants in the form of two-dimensional islands may be essential for the chain propagation reactions. In this study, the e-beam irradiation effects on molecular dissociation and desorption are investigated in the electron energy range of 5-70 eV. Preliminary report of these effects was given recently,@footnote 1@ and a detailed account will be presented in this paper. @FootnoteText@ @footnote 1@ P. Chuang, Y.L. Chan, S.-H. Chien, R. Klauser and T.J. Chuang, Chem. Phys. Lett. 354,179 (2002).