TABLE V: Raman vibrational peak frequencies (cm − $^{1}$): Experimental data and computational values for the HSCH$_{2}$COOH, SCH$_{2}$COOH, HSCH$_{2}$COO − and SCH$_{2}$COO − on the Au(111) surface. The calculated frequencies which are the closest to the experimental ones are underlined. frequencies ω$_{1}$ ω$_{2}$ ω$_{3}$ ω$_{4}$ ω$_{5}$ ω$_{6}$ ω$_{7}$ ω$_{8}$ Exp. data 8 575 665 763 905 930 1387 1597 1711 Au-HSCH$_{2}$COOH 575 653 745 881 - 1409 - 1733 Au-SCH$_{2}$COOH 596 670 725 872 - 1396 - 1738 Au-HSCH$_{2}$COO − 592 619 734 - 929 1369 1627 - Au-SCH$_{2}$COO − 598 638 822 - 838 1366 1577 - were calculated for the most stable configurations at 0.25ML. The calculated frequencies which are the closest to the experimental ones are underlined. The Raman scattering is limited to the center of the Brillion zone, and the vibrational frequencies are calculated at ¯ Γ point. As shown in Fig. 5a, the frequency ω$_{1}$ (575cm − $^{1}$, 575cm − $^{1}$) (the first number stands for the experimentally measured frequency and the second one is the corresponding theoretical one, which is underlined in Table V) is the vibration of the S-C1 and the C1-C2 stretches (the O1 and O2 atoms displace slightly). The theoretical counterpart suggests that the fre- quency 575cm − 1 comes from the HSCH$_{2}$COOH on the gold surface. Fig. 5b indicates that the mode ω$_{2}$ (665cm − $^{1}$, 670cm − $^{1}$) is attributed to the C1-S vibration of the SCH$_{2}$ COOH on the substrate. The frequency ω$_{3}$ (763cm − $^{1}$, 745cm − $^{1}$) corresponds to the C1-S stretch of the HSCH$_{2}$COOH on the surface, where the O1 atom displaces slightly (Fig. 5c). The mode ω$_{4}$ (905cm − $^{1}$, 881cm − $^{1}$) is ascribed to the stretching vibration of the C-COOH in the HSCH$_{2}$COOH molecule on the Au(111) (Fig. 5d). ω$_{5}$ (930cm − $^{1}$, 929cm − $^{1}$) corresponds to the C-COO − stretching vibration for the HSCH$_{2}$COO − on the gold surface (Fig. 5e). The frequency ω$_{6}$ (1387cm − $^{1}$, 1396cm − $^{1}$) is due to the vibration of the COOH of the SCH$_{2}$ COOH on the gold surface (the C1 atom moves slightly, see Fig. 5f). The mode ω$_{7}$ (1597cm − $^{1}$, 1577cm − $^{1}$) can be assigned to this COO − stretch in the SCH$_{2}$COO − (Fig. 5g), which in- dicates that after the dissociation of the mercaptan hydrogen atom and the deprotonation of the carboxylic acid group, some original HSCH$_{2}$COOH molecules on the surface have 14