THE INFRARED BAND STRENGTHS OF H2O, CO AND CO2 IN LABORATORY SIMULATIONS OF ASTROPHYSICAL ICE MIXTURES

Infrared spectroscopic observations toward objects obscured by dense c loud material show that H2O, CO and, likely, CO2 are important constit uents of interstellar ice mantles. In order to accurately calculate th e column densities of these molecules, it is important to have good me asurements of their infrared band strengths in astrophysical ice analo gs. We present the results of laboratory experiments to determine thes e band strengths. Improved experimental methods, relying on simultaneo us independent depositions of the molecule to be studied and,of the do minating ice component, have led to accuracies better than a few perce nt. Furthermore, the temperature behavior of the infrared band strengt hs of CO and H2O are studied. In contrast with previous work, the stre ngths of the CO, CO2, and H2O infrared features are found to depend on ly weakly on the composition of the ice matrix, and the reversible tem perature dependence of the CO band is found to be weaker than previous ly measured for a mixture of CO in H2O.