The thermal decomposition of 1-pentanol and 2-methyl-1-butanol on clean Si(100)-2 x 1 in an ultrahigh vacuum has been examined using temperature programmed desorption, intergrated desorption mass spectrometry, and low-energy electron diffraction. The results show that the alkoxy species formed on Si(100) are stable up to temperatures of about 480 K. Above 500 K, the alkoxy species decompose on Si(100) vial the gamma-hydrogen elimination mechanism to yield alkene in the gas phase, together with adsorbed hydrogen. The H-2 gas is evolved by the recombinative desorption of hydrogen atoms that are generated by the adsorption of alcohols and/or the decomposition of alkoxy species. The, H-2 thermal desorption exhibits a peak near 800 K, which indicates that the H-2 gas is. evolved from the monohydride phase on Si(100). (C) 2003 American Vacuum Society.