AVS 49th International Symposium
    Surface Science Monday Sessions
       Session SS1-MoM

Paper SS1-MoM5
Experimental and Theoretical Characterization of the Vibrational Properties of Aminocarbyne Surface Intermediates

Monday, November 4, 2002, 9:40 am, Room C-108

Session: Adsorption and Chirality
Presenter: M. Trenary, University of Illinois at Chicago
Authors: B. Chatterjee, University of Illinois at Chicago
D.H. Kang, University of Illinois at Chicago
P. Mills, North Central College
M. Trenary, University of Illinois at Chicago
Correspondent: Click to Email
Density functional theory (DFT) calculations and measurements using reflection absorption infrared spectroscopy have been used to characterize aminocarbynes on a Pt(111) surface. The three aminocarbynes considered are CNH@sub 2@, CNHCH@sub 3@ and CN(CH@sub 3@)@sub 2@. The CNH@sub 2@ species, known simply as aminocarbyne or as aminomethylidyne, is formed from HCN, methyl amine, or the hydrogenation of surface CN. Methylaminocarbyne, CNHCH@sub 3@, can be formed from the N-protonation of methyl isocyanide (CNCH@sub 3@) or from the partial dehydrogenation of dimethyl amine, HN(CH@sub 3@)@sub 2@. Dimethylaminocarbyne, CN(CH@sub 3@)@sub 2@, is formed from the decomposition of trimethylamine, N(CH@sub 3@)@sub 3@. The DFT calculations were based on a model consisting of only two Pt atoms, as would be appropriate for bonding at a two-fold bridge site. Gaussian 98 with the B3LYP functional and a 6-311G** basis set along with effective core potentials for the Pt atoms was used. The calculations converged and optimized to reasonable geometries. For example, Pt@sub 2@CNH@sub 2@ converged to a C@sub 2v@ symmetry structure with a CN bond length of 1.32 Å with calculated frequencies (using the appropriate scale factor of 0.9613) for the @nu@(CN), @delta@(NH@sub 2@), and @nu@@sub s@(NH) fundamentals of 1393, 1564, and 3407 cm@super -1@, respectively, compared to experimental values for CNH@sub 2@ on Pt(111) of 1323, 1567, and 3363 cm@super -1@. The calculations successfully reproduce not only the measured vibrational frequencies, but also the relative intensities and the measured shifts that occur with various isotopic substitutions. Calculations using larger Pt clusters, which are much more time consuming, lead to only modest improvements. The results suggest that the internal vibrations of polyatomic adsorbates can be successfully calculated using models of the surface that are surprisingly simple.