TOF-SIMS investigation of interactions between water and nitrogen at 15 K

TOF-SIMS is used to characterize the van der Waals complex formed on the surface by adsorption of H2O on N2 molecules. For N2 adsorption on the amorphous solid water, the H+ yield sputtered from H2O is markedly enhanced with increasing coverage while the H3O+ yield decays monotonically. This is because the H+ ion is created efficiently during collisions between H2O and N2 molecules. This occurs provided that the N2 layer (<1 ML) wets the H2O surface and no thick N2 layer grows on the H2O layer. In the case of amorphous solid water prepared at 15 K, the N2 molecules are incorporated in the inner pores preferentially and then cover the outermost surface after saturation, suggesting the high mobility of the N2 molecule on the water surface. A pure H2O film is hardly grown on the N2 layer (50 ML) up to the H2O coverage of 100–150 ML due to intermixing.