Cycloaddition chemistry of thiophene on the silicon (111)-7x7 surface

The mechanism of the cycloaddition reaction between thiophene and Si(111)-7x7 has been investigated using thermal desorption spectroscopy (TDS), high resolution electron energy loss spectroscopy (HREELS), electronic electron energy loss spectroscopy (EELS), scanning tunneling microscopy (STM), and PM3 semiempirical calculations. The results show that thiophene binds on Si(111)-7x7 through a [4+2] cycloaddition reaction between the 2, 5 C-atoms of thiophene and the adjacent adatom-rest atom pairs on Si(111)-7x7. Semiempirical PM3 calculations based on the cluster model further confirm this di-sigma bonding configuration. A stepwise surface diradical mechanism has been proposed to account for the regioselective [4+2] cycloaddition reaction. (C) 2001 American Institute of Physics.