  The surfaces of icy moons are primarily composed of water ice that can be
mixed with other compounds, such as carbon dioxide. The carbon dioxide (CO$_2)$
stretching fundamental band observed on Europa and Ganymede appears to be a
combination of several bands that are shifting location from one moon to
another. We investigate the cause of the observed shift in the CO$_2$
stretching absorption band experimentally. We also explore the spectral
behaviour of CO$_2$ ice by varying the temperature and concentration.}
%H$_2$O:CO$_2$ deposition ratios. We analyzed pure CO$_2$ ice and ice mixtures
deposited at 10 K under ultra-high vacuum conditions using Fourier-transform
infrared (FTIR) spectroscopy and temperature programmed desorption (TPD)
experiments. Laboratory ice spectra were compared to JWST observation of
Europa's and Ganymede's leading hemispheres. The simulated IR spectra were
calculated using density functional theory (DFT) methods, exploring the effect
of porosity in CO$_2$ ice. Pure CO$_2$ and CO$_2$-water ice show distinct
spectral changes and desorption behaviours at different temperatures, revealing
intricate CO$_2$ and H$_2$O interactions. The number of discernible peaks
increases from two in pure CO$_2$ to three in CO$_2$-water mixtures.
