Interactions of D2O with CO and CO2 molecules at cryogenic temperatures

On the basis of the matrix effect of secondary-ion mass spectrometry (SIMS), the intermolecular interactions between D2O and hydrophobic molecules have been investigated at temperature of 15 K. The D+ yield is found to be enhanced markedly relative to the D3O+ yield when the D2O molecule forms a complex with the CO or CO2 molecules on the surface. The CO molecules are incorporated in the inner pores of amorphous solid water and then cover the outermost surface facing to the vacuum, which is followed by the 3D-island growth on it. A similar result is obtained for the adsorption of the CO2 molecule but the filling of the inner pores is not complete due to the lower mobility of the CO2 molecule. The D2O film grows on the CO2 layer, but a pure D2O film is hardly formed on the CO layer due to the occurrence of intermixing.