Adsorption of 2-propanol, (CH3)(2)CHOH, on a Si(111)-7x7 surface was studied by scanning tunneling microscopy. (CH3)(2)CHOH adsorbs equally on the faulted and unfaulted half unit cells by forming Si-OCH(CH3)(2) and Si-H on an adatom and rest atom pair. Si-OCH(CH3)(2) is consecutively increased in each half unit cell, and the adsorption is saturated when every half unit cell has three Si-OCH(CH3)(2), which corresponds to 0.5 of the adatom coverage. The sticking probability for the dissociation of (CH3)(2)CHOH is independent of the adatom coverage from 0 to 0.4, but it depends on coverage at higher than 0.4. By counting the darkened adatoms, Si-OCH(CH3)(2) on the center adatom (m) and that on the corner adatom (n), it was found the m/n ratio is ca. 4 for the first dissociation of (CH3)(2)CHOH in virgin half unit cell, but it becomes ca. 1.9 and 1.8 when two and three Si-OCH(CH3)(2) are contained in a half unit cell. This result reveals that the dissociation probability of (CH3)(2)CHOH at the adatom-rest atom pair site is influenced by the nearest Si-OCH(CH3)(2) in the half unit cell. (C) 2004 American Institute of Physics.