Self-assembled monolayers of alkanethiolate on gold were shown to desorb or be replaced from the gold surface by exposure to H2S vapor. Under the same conditions, the desorption occurred faster with shorter chain length thiols than with longer ones. The thiolate moiety desorbed mainly in the form of a free thiol, which underwent various structural reorganizations depending on the chain length as well as the terminal functional group it carries. For nonpolar. methyl-terminated thiols, the assembly either randomized to give a disordered liquid state (for chain length