The motion of alkanethiol ligand molecules self-assembling on nano- scale gold particles was studied by measuring the spin-lattice relaxation time (T_1) and spin-spin relaxation time (T_2). Two types of ligands, Py(CH_2)_(12)SH and CH_3(CH_2)_7SH as well as their mixtures of different ratio are employed in this work. NMR relaxation times of four protons at different positions versus steric effect and mixing proportion in ligand mixtures were monitored. Due to different influences of various factors, each of these protons show different motion characteristics. For the ligands connected with Au particle, NMR T_1 and T_2 at position 2 and 3 decrease whereas those at position 1 and 4 increase. For the mixed ligands, with increasing of Py(CH_2)_ (12)SH content, T_1 and T_2 at position 1, 2, 3 and T_1 at position 4 decrease, while NMR T_2 at position 4 increases. However, protons at different positions have different T_1 and T_2 variation speeds. The proton at position 2, due to its special location, has the largest flexibility in the motion with ligands mixing ratio PY:C_8 = 1:1 [PY represents Py(CH_2)_(12)SH; C_8 represents CH_3(CH_2)_7SH]. The experimental results also show that T_1 is always greater than the corresponding T_2, which indicates that ligands is in low frequency motion region in the system investigated.

Key words: MERCAPTO COMPOUNDS, GOLD, NANOPHASE MATERIALS, RELAXATION