The infrared band strengths of CH3OH, NH3 and CH4 in laboratory simulations of astrophysical ice mixtures

Results from groundbased observations and the Infrared Space Obseratory (IS O) indicate that CH3OH, NH3 and CH4 are important constituents of interstel lar ice mantles. In order to accurately calculate the column densities of t hese molecules, it is important to have good measurements of their infrared band strength in astrophysical ice analogs. Band strength measurements of CH3OH and CH4 are presented showing that they depend only weakly on the com position of the ice matrix and the temperature. On the other hand, the umbr ella mode of NH3 does show a significant decrease when dilluted in H2O ice. For this reason the original estimates of the abundance of NH3 in interste llar ice need to be revised upward by 30%.