A selective [4+2]-like cycloaddition of alpha,beta-unsaturated ketone on Si(111)-7X7

• Published in: Surface science 2007-08, Vol.601 (16), p.3293-3302
• Main Authors: Tang, Hai Hua, Cai, Ying Hui, Ning, Yue Sheng, Lai, Yee Hing, Xu, Guo Qin
• Format: Article
• Language: English
• ISSN: 0039-6028
• DOI: 10.1016/j.susc.2007.05.018

The interaction of ethyl vinyl ketone (EVK) with Si(111)-7X7 has been investigated using high-resolution electron energy loss spectroscopy (HREELS), X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculations. The disappearance of both stretching vibrations of CH2 (3099cm-1) and CO (1684cm-1) coupled with the appearance of new CC stretching mode (1660cm-1) in the HREELS spectra of chemisorbed EVK clearly demonstrates the direct involvement of conjugated CC and CO bonds to form a SiC1H2C2HC3(C4H2C5H3)OSi surface species via [4+2]-like cycloaddition in a highly selective manner. In addition, XPS studies show that the C1s binding energies of C1/C2 and C3 upon chemisorption display chemical downshifts of 0.8eV and 2.2eV, respectively, further confirming the proposed [4+2]-like cycloaddition reaction for the EVK/Si(111)-7X7 system. DFT theoretical calculations suggest that the proposed [4+2]-like cycloadduct is thermodynamically most favorable.