D2O Ice on Controlled Wettability Self-Assembled Alkanethiolate Monolayers: Cluster Formation and Substrate−Adsorbate Interaction

Abstract

Infrared reflection−absorption spectroscopy is used to investigate thin (1−200 A average thickness) overlayers of D2O ice deposited in ultrahigh vacuum on controlled wettability self-assembled monolayers. The monolayers were derived from mixed solutions of HS(CH2)15CH3 and HS(CH2)16OH, making it possible to examine the whole range of samples from fOH = 0.0 to fOH = 1.0, where fOH denotes the molar fraction of OH-terminated thiols in the preparation solution. This paper focuses on the interaction between the ice and the monolayer. It is shown that water molecules do not penetrate into the monolayer but that two types of interaction with the chain-terminating groups occur: hydrogen bond formation with surface hydroxyls and weak dipole−dipole interaction with surface methyls. For surfaces with fOH < 0.3, the latter interaction causes the free OD mode, normally observed at 2729 cm-1, to shift to 2704 cm-1, thereby providing a spectral signature feature whose intensity is directly proportional to the relative...