Summary:

Ices formed on the surfaces of dust grains in the interstellar medium consists primarily of H₂O, but also other molecules such as CO, CO₂ and CH₃OH. The dangling O-H bands of H₂O at frequencies around 3630-3720 cm^-1 provide information on the structural properties of amorphous water ices, as it indicates that either a vacuum interface or an interface with a non-water neighboring molecule is present.

In this work, the role played by segregation level, mixing ratio, and type of interface present for the IR peak positions of the dangling O-H bands and the CO₂ bend and stretch bands in mixed H₂O/CO₂ ices is studied computationally. Different structure generation methods are used to generate the analyzed structures, with the aim of covering a range of possible structures representative for interstellar ices.

The study shows that the local environment of a molecule has significant impact on the dangling O-H and CO₂ stretch band. In particular, the mixing ratio and type of interface come out as influential, while density and temperature are shown to have an negligible effect on the peak positions.

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