Interaction of coadsorbed $CH3Cl$ and $D2O$ layers on Pd(111) studied by sum frequency generation Available to Purchase

Adsorption of methyl chloride and coadsorption of $CH3Cl$ and $D2O$ on Pd(111) surfaces at $T=100K$ have been studied under ultrahigh-vacuum conditions using femtosecond sum frequency generation (SFG) spectroscopy in the spectral regions of CH and OD bands. On the bare Pd(111) substrate, the $CH3Cl$ coverage dependence of the resonant SFG signal is consistent with a progressive molecular rearrangement starting at half saturation followed by the growth of two ordered monolayers in which the molecular axes are perpendicular to the surface. When $CH3Cl$ is adsorbed on top of predeposited $D2O$ on Pd(111), the SFG signals as a function of the $CH3Cl$ exposure indicate that methyl chloride is adsorbed onto $D2O$ through hydrogen bonding. On the contrary when the adsorption order is reversed the strong decrease of the $CH3$ signal as a function of the $D2O$ exposure is explained by assuming that water molecules penetrate inside the $CH3Cl$ layers, leading to the formation of disordered $CH3Cl$ clusters. In all cases a nonresonant contribution due to molecular adsorption is observed and it shows a dependence upon surface structure and coverage significantly different from that of the resonant vibrational bands.