Infrared spectra of CO2 in H2O : CH3OH : CO2 icy mixtures

We have studied by laboratory infrared spectroscopy the profile of the CO2 absorption bands in different H2O:CH3OH:CO2 mixtures. Icy mixtures have bee n accreted on a substrate at 12.5 K inclined of 45 degrees with respect to the infrared beam of the spectrometer. Spectra have been taken with the ele ctric vector of the infrared beam parallel (P polarized) and perpendicular (S polarized) to the plane of incidence. The samples have been warmed up an d spectra have been taken at different temperatures. We confirm CO2 segrega tion after warm-up. Furthermore we find that when segregation occurs the pr ofile of CO2 bands are different in the two different polarization cases. A s shown by Baratta et al. (2000) this means that these laboratory spectra c annot be directly compared to the astronomical spectra.