The Infrared Band Strengths of H2o, Co and Co2 in Laboratory Simulations of Astrophysical Ice Mixtures

TL;DR

This study provides precise laboratory measurements of infrared band strengths for H2O, CO, and CO2 in astrophysical ice analogs, improving the accuracy of interstellar molecule column density calculations.

Contribution

The paper introduces improved experimental methods for measuring infrared band strengths with higher accuracy and examines their temperature dependence in astrophysical ice analogs.

Findings

Infrared band strengths depend weakly on ice composition.

Temperature effects on CO band strengths are weaker than previously thought.

Achieved measurement accuracy better than a few percent.

Abstract

Infrared spectroscopic observations toward objects obscured by dense cloud material show that H$_2$O, CO and, likely, CO$_2$ are important constituents of interstellar ice mantles. In order to accurately calculate the column densities of these molecules, it is important to have good measurements of their infrared band strengths in astrophysical ice analogs. We present the results of laboratory experiments to determine these band strengths. Improved experimental methods, relying on simultaneous independent depositions of the molecule to be studied and of the dominating ice component, have led to accuracies better than a few percent. Furthermore, the temperature behavior of the infrared band strengths of CO and H$_2$O are studied. In contrast with previous work, the strengths of the CO, CO$_2$, and H$_2$O infrared features are found to depend only weakly on the composition of the ice matrix, and the reversible temperature dependence of the CO band is found to be weaker than previously measured for a mixture of CO in H$_2$O.