Dynamics of water dissociation and ice nucleation on Cu(111) and O/Cu(111)

In this thesis, I present an investigation of the interactions of water molecules with a single crystal Cu(111) surface, examined using a molecular beam, ultra-high vacuum surface science techniques and Reflection Absorption Infrared Spectroscopy (RAIRS). Both water dissociation and water ice nucleation are studied on clean Cu(111) and partially oxidized O/Cu(111). First, I discuss D2O dissociation on a clean Cu(111) surface. In these experiments, the initial dissociative sticking coefficients are obtained while controlling the translational energy as well as vibrational energy, added to the water molecules via infrared laser excitation. I present the resulting trend in initial sticking coefficients without laser excitation, which points towards two separate pathways: precursor-mediated dissociation at lower kinetic energies and direct dissociation at higher kinetic energies. I show that the determination of vibrational efficacy for water dissociation on Cu(111) is challenging due to the stickiness of water molecules. A possible solution to this issue is suggested and examined, however coming with its own complications. Second, an in-depth study of the mechanism of water dissociation on partially oxidized O/Cu(111) is discussed. Using RAIRS and isotope labelling of oxygen atoms (16O, 18O), I show that the water dissociation reaction proceeds via a hydrogen transfer mechanism, where a water molecule loses a hydrogen atom to an oxygen atom on the surface, which results in the creation of two chemisorbed hydroxyl species: 16OH(ads) and 18OH(ads). However, due to the presence of molecular water at a surface temperature of 180 K, an unexpected hydrogen exchange is observed between the hydroxyl species and adsorbed H2O(ads). This exchange results in complete replacement of one oxygen isotope and the observation of just one hydroxyl isotopologue remaining on the surface. Last, I describe an investigation of the process of ice nucleation on the bare Cu(111) and partially oxidized O/Cu(111) surfaces. The infrared spectra of the D2O ice differ significantly between the two surfaces. This is attributed to the contrast in chemical environments, with bare Cu(111) being hydrophobic and O/Cu(111) being hydrophilic. On O/Cu(111), a new infrared absorption peak is reported. I assign this peak to the stretch of an O-D bond of D2O molecules pointing towards the surface, due to interactions with chemisorbed hydroxyl species. In addition, major disparities are shown between low-coverage and high-coverage of water ice, especially on the partially oxidized O/Cu(111) surface. The evolution of the ice structure from the low-coverage towards the high-coverage regime is discussed. Both the destructive and non-destructive pathways examined in this thesis arrive at an interesting conclusion. The interactions of water molecules with the copper surface show a complex interplay of processes, the mechanisms of which are prone to be overlooked if careful experimentation is not un