Ja. Jensen et al., DIRECT CHEMISORPTION SITE SELECTIVITY FOR MOLECULAR HALOGENS ON THE SI(111)-(7X7) SURFACE, Physical review letters, 76(8), 1996, pp. 1388-1391
Direct chemisorption site preferences within the Si(111)-(7 x 7) unit
cell are examined for F-2, Cl-2, and Br-2. Abstractive chemisorption,
which produces a single chemisorbed halide atom, always prefers center
adatom adsorption, indicating that the site with the lowest electron
density is the more reactive. Dissociative chemisorption, which produc
es a pair of chemisorbed halide atoms, shows an extreme preference for
the closest neighboring pair of center adatoms. The notion of a stepw
ise direct chemisorption mechanism is upheld by these results.