Studies of binary layered CH3OH/H2O ices adsorbed on a graphite surface

Reflection absorption infrared spectroscopy (RAIRS) and temperature programmed desorption (TPD) have been used to investigate binary layered ice systems consisting of methanol deposited on top of various thicknesses of water ice, grown on an underlying graphite surface. RAIRS shows that there is no difference between the RAIR spectra recorded for pure ices and that recorded for the layered ices, suggesting that there is no discernible interaction between the layers during adsorption. However, annealing the ice layers leads to intermixing, as evidenced by a 50 cm-1 downshift of the O-H stretching frequency of the mixed ice, compared to that expected from a simple combination of the pure water and pure methanol O-H stretching bands. TPD shows several new species when compared with TPD spectra for pure ices, confirming that mixing of the ice layers occurs on heating. A TPD peak that can be assigned to the trapping of methanol within the water ice is observed. TPD peaks for the desorption of monolayer and multilayer methanol are also observed.