Predicting the infrared band profiles for CO2 cloud particles on Mars

The present contribution describes the influence of the properties of potential martian CO2 cloud particles on their mid-infrared (IR) extinction spectra, with the goal to provide a reference for possible future IR extinction cloud studies on Mars. The focus lies on the understanding of the band shape of the antisymmetric stretching vibration at about 4.3 μm. For this purpose, modelling of particle spectra with the vibrational exciton model, the discrete dipole approximation, and density functional calculations are combined with experimental results recorded in a collisional cooling cell. The effect of particle size, shape, and architecture on IR extinction spectra is studied for pure CO2 particles, H2O–CO2 core–shell particles with and without a molecularly mixed interface, H2O particles partially engulfed by CO2 patches, and mineral dust–CO2 core–shell particles. The results show how IR extinction spectra might be helpful in the identification of the martian cloud properties in particular if other complementary data is available.