Issue 18, 2011

Vibrational excitation of adsorbed molecules by photoelectrons of very low energy: acrylonitrile on Cu (100)

Abstract

In this study, we report on a powerful method of primary photoelectron scattering by adsorbed species. Specifically, threshold-energy (Ekin,max < 0.5 eV) two-photon photoelectrons (2PPE) are used to probe acrylonitrile (ACN) molecules chemisorbed onto a Cu(100) substrate, held at room temperature. This has proven to constitute a perfect tool to reveal the ACN vibrational modes in the chemisorbed state. From the dynamics of the directional (perpendicular to the copper surface) electron energy loss we conclude that only a few fundamental vibrational motions of adsorbed ACN are excited, namely the C[double bond, length as m-dash]C, C[triple bond, length as m-dash]N and C–H stretch modes. From the excitation probability spectra threshold energies, Eth, of these modes was extracted: Eth(C[double bond, length as m-dash]C) = 182(15) meV, Eth(C[triple bond, length as m-dash]N) = 248(16) meV—which are shifted noticeably from the equivalent gas phase values; and Eth(C–H) ∼360–380 meV—which varies only marginally from the gas phase value. The interpretation of the excitation spectra suggests that the di-σ adsorption configuration of the terminal C- and N-atoms dominates, which agrees well with the orientation and bindings predicted in Density Functional Theory (DFT) calculations. Consistent with this is the observation that the contribution to the 2PPE excitation spectra from the C–H stretch motion is by far the largest, which are not directly affected by chemisorption bonding.

Graphical abstract: Vibrational excitation of adsorbed molecules by photoelectrons of very low energy: acrylonitrile on Cu (100)

Supplementary files

Article information

Article type
Paper
Submitted
20 Sep 2010
Accepted
22 Feb 2011
First published
14 Mar 2011

Phys. Chem. Chem. Phys., 2011,13, 8475-8484

Vibrational excitation of adsorbed molecules by photoelectrons of very low energy: acrylonitrile on Cu (100)

J. Tornero, H.H. Telle, G. García and A. González Ureña, Phys. Chem. Chem. Phys., 2011, 13, 8475 DOI: 10.1039/C0CP01869D

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