Photoinduced localized atomic reaction (LAR) of 1,2-and 1,4-dichlorobenzene with Si(111) 7x7

We report a comparative study of the photoinduced localized atomic reaction, LAR, of 1,2- and 1,4-dichlorobenzene (1,2- and 1,4-diClPh) on Si(111) 7x7, studied by scanning tunneling microscopy (STM). We observe different chlorine nearest-neighbor separations for the Cl-Si photoformed chemical "imprints" for the two adsorbates; the most probable separation of neighboring Cl's in the case of 1,2-dichlorobenzene being 8 +/- 3 Angstrom, whereas that for 1,4-dichlorobenzene is 14 +/- 3 Angstrom. These differing separations can be understood if the two C-Cl bonds in the respective adsorbates extend roughly linearly to chlorinate a nearby Si dangling-bond; for 1,2 diClPh the two C-Cl bonds are at 60 degrees to one another leading to the chlorination of closely neighboring Si, whereas for 1,4 diClPh the two C-Cl bonds are at similar to 180 degrees leading to chlorination of sites twice as far apart, located to either side of the 1,4 diClPh adsorbate. (C) 2000 American Institute of Physics. [S0021-9606(00)70124-3].