AVS 49th International Symposium
    Surface Science Wednesday Sessions
       Session SS-WeM

Paper SS-WeM1
Surface Vibrational Spectroscopy Beyond the Harmonic Approximation: Experiments and ab initio Calculations of Ethoxy Adsorbed on Cu(100)

Wednesday, November 6, 2002, 8:20 am, Room C-112C

Session: New Opportunities and Technique Innovations
Presenter: M.P. Andersson, Lund University, Sweden
Authors: M.P. Andersson, Lund University, Sweden
P. Uvdal, Lund University, Sweden
Correspondent: Click to Email
We compare high sensitivity experimental reflection-absorption IR spectra of ethoxy adsorbed on Cu(100) with ab initio calculations. The high sensitivity allows for detection of binary combinations of CH bend modes, i.e. overtones and combination bands. As their presence cannot be explained using a strictly harmonic approximation, we include anharmonic effects in the ab initio treatment as well. Calculations at the harmonic level are performed for an ethoxy-Cu17 cluster with a hybrid DFT method. Anharmonic effects are computationally more demanding and are therefore calculated for the free ethanol molecule using the same method and basis set as for the cluster. The anharmonic effects are then added through a standard expression involving third and fourth derivatives of the energy. The method allows for inclusion of both intramode anharmonicity and anharmonic resonance effects such as Fermi resonances due to accidental degeneracy. The experimental spectrum is reproduced in detail, including CH bend overtones and combination bands in resonance with CH stretch fundamentals. The mean absolute deviation is only 10 cm-1 and all intensities are also very well reproduced.