Aerosol particles of molecular substances are generated in a collisional cooling cell. The injection of a warm sample gas into the cold bath gas of the cooling cell (T > 4K) leads to the particle formation. The particle size and shape can be controlled by the bath gas temperature and the bath gas pressure. The vibrational dynamics of the generated aerosols is investigated with infrared spectroscopy. This allows to learn more about the relation between the properties of the particles and the nature of the intermolecular interactions that hold them together. The main focus lies on the influence of the size and the shape of the particles on the observed band structures in the infrared spectra. Comparisons with quantum chemical calculations, exciton models and continuum models help to understand the observed spectral patterns. You learn something about the generation of aerosols with cooling techniques, rapid-scan infrared spectroscopy, the vibrational dynamics of the aerosol particles (size/shape dependent resonance phenomena, scattering effects) and its relation to the intermolecular interactions.