The formation of an enynic-like intermediate in diacetylene binding on Si(1 0 0)-2 × 1

The covalent attachment of diacetylene (HCC–CCH) and the formation of a CC–CC structure on Si(1 0 0) have been investigated using high-resolution electron energy loss spectroscopy (HREELS) and density functional theory (DFT) calculations. The HREELS spectrum of the chemisorbed monolayer shows the coexistence of Csp–H and Csp2–H stretching modes coupled with the concurrent observation of the CC and CC stretching modes. The experimental results unambiguously demonstrate a [2 + 2]-like cycloaddition mechanism for diacetylene chemisorption on Si(1 0 0) through the binding between one of the CC groups and a Si dimer, consistent with the prediction of DFT calculations.