Interaction of NaI with solid water and methanol.

The interaction of NaI with amorphous solid water (ASW) and methanol (MeOH) has been investigated with metastable impact electron spectroscopy (MIES), UPS(HeI), and temperature programmed desorption (TPD). We have studied the electron emission from the ionization of the highest-lying states of H(2)O, CH(3)OH, and of 5pI. We have prepared NaI layers on ASW (MeOH) films at about 105 K and annealed them up to about 200 K. Surface segregation of iodide is observed in ASW, as predicted for NaI aqueous solutions. On the other hand, surface segregation is not observed in MeOH, again as predicted for the interaction of NaI with liquid methanol. Electronic properties (ionization potentials, optical band gaps) and water binding energies are reported and are analyzed on the basis of available DFT results for hydrated NaI clusters.

Interaction of NaCl with solid water.

The interaction of NaCl with solid water, deposited on tungsten at 80 K, was investigated with metastable impact electron spectroscopy (MIES) and ultraviolet photoelectron spectroscopy (UPS) (He I). We have studied the ionization of Cl(3p) and the 1b(1), 3a(1), and 1b(2) bands of molecular water. The results are supplemented by first-principles density functional theory (DFT) calculations of the electronic structure of solvated Cl(-) ions. We have prepared NaCl/water interfaces at 80 K, NaCl layers on thin films of solid water, and H(2)O ad-layers on thin NaCl films; they were annealed between 80 and 300 K. At 80 K, closed layers of NaCl on H(2)O, and vice versa, are obtained; no interpenetration of the two components H(2)O and NaCl was observed. However, ionic dissociation of NaCl takes place when H(2)O and NaCl are in direct contact. Above 115 K solvation of the ionic species Cl(-) becomes significant. Our results are compatible with a transition of Cl(-) species from an interface site (Cl in direct contact with the NaCl lattice) to an energetically favored configuration, where Cl species are solvated. The DFT calculations show that Cl(-) species, surrounded by their solvation shell, are nevertheless by some extent accessed by MIES because the Cl(3p)-charge cloud extends through the solvation shell. Water desorption is noticeable around 145 K, but is not complete before 170 K, about 15 K higher than for pure solid water. Above 150 K the NaCl-induced modification of the water network gives rise to gas phase like structures in the water spectra. In particular, the 3a(1) emission turns into a well-defined peak. This suggests that under these conditions water molecules interact mainly with Cl(-) rather than among themselves. Above 170 K only Cl is detected on the surface and desorbs around 450 K.

The interface between benzenes (C6H6;C6H5Cl;2-C6H4OHCl) and amorphous solid water studied with metastable impact electron spectroscopy and ultraviolet photoelectron spectroscopy (HeI and II).

Interfaces between films of benzenes (C(6)H(6);C(6)H(5)Cl;2-C(6)H(4)OHCl) and solid H(2)O on tungsten substrates were studied between 80 and 200 K with metastable impact electron spectroscopy (MIES) and ultraviolet photoelectron spectroscopy [UPS(HeI and II)]. The following cases were studied in detail: (i) Adsorption of the benzenes on solid water in order to simulate their interaction with ice particles, and (ii) deposition of water on benzene films in order to simulate the process of water precipitation. In all cases the prepared interfacial layers were annealed up to 200 K under in situ control of MIES and UPS. The different behavior of the interfaces for the three studied cases is traced back to the different mobilities of the molecules with respect to that of water. The interaction between H(2)O and the benzenes at the interfaces is discussed on the basis of a qualitative profile for the free energy of that component of the interface which has the larger mobility. Possible implications of the present results for atmospheric physics are briefly mentioned.

Electron solvation by polar molecules: the interaction of Na atoms with solid methanol films studied with MIES and density functional theory calculations.

The interaction of Na atoms with CH(3)OH films was studied with metastable impact electron spectroscopy (MIES) under UHV conditions. The films were grown at 90(+/-10) K on tungsten substrates and exposed to Na. Na-induced formation of methoxy (CH(3)O) species takes place, and Na atoms become ionized. At small Na exposures the outermost solvent layer remains largely intact as concluded from the absence of MIES signals caused by the reaction products. However, emission from CH(3)O, located at the film surface, occurs at larger exposures. In the same exposure range also Na species can be detected at the surface. The spectral feature from 3s Na ionization occurs at an energetic position different from that found for metals or semiconductors. The results are compared with density functional theory calculations [see Y. Ferro, A. Allouche, and V. Kempter, J. Chem. Phys. 120, 8683 (2004), preceding paper]. Experiment and theory agree in the energetic positions of the main spectral features from the methanol and sodium ionization. The calculations suggest that the 3s Na emission observed experimentally originates from solvated 3s electrons which are located far from the Na core and become stabilized by solvent molecules. The simultaneous emergence of emission from CH(3)O and from solvated 3s electrons suggests that the delocalization and, consequently, the solvation play an important role in the Na-induced formation of CH(3)O from CH(3)OH.