Paper SS1+NC-ThA8
Isotopic Effects in the Mixing Between Surface and Bulk Molecules at the Surface of Amorphous Solid Ice Studied by FTIR and DFT Calculations

Thursday, October 23, 2008, 4:20 pm, Room 207

We have studied the exchange between surface and bulk molecules on amorphous solid ice using infrared vibrational spectroscopy. Intact molecules are grown in a layer by layer fashion, on Cu(100), allowing the formation of isotopically uniform layers at 84 K. A bulk layer consisting of 3-5 bilayers of ice of isotope A was exposed to 0.15 monolayers of isotope B. Three different water isotopes were used in this study, H₂¹⁶O, D₂¹⁶O and H₂¹⁸O. By studying the free O-H(D) stretch, present only at the ice surface, all isotopes could be spectroscopically identified. In particularly, the decrease of isotope B could be monitored, along with the concomitant increase of isotope A, as a function of temperature. It is observed that mixing between surface and bulk water starts already at 100K. There are also a clear difference between the different isotopes. H/D exchange is observed and will be discussed. The vibrational data is interpreted with the aid of DFT cluster calculations.