Knowledge Bank

Cryogenic aerosols are generated via homogeneous nucleation in a flowing mixture of condensible and non-condensible gases at low temperature. FTIR spectra of the resulting cryo-cloud display features due to the interaction of scattering and absorption processes. Mie scattering calculations used in conjunction with the FTIR results indicate the spectra are highly sensitive to the particle size distribution. Compelling spectroscopic evidence indicates that $C2H2$ aerosol, formed in cold He at 95K, is in the high temperature cubic phase despite a solid-solid phase transition to the orthorhombic phase observed at 133K in the bulk solid. Mixed aerosols, composed primarily of Xe, provide the opportunity to observe diffusion in micro-particles and afford a gas-phase analogy to matrix isolation. Moreover, competition between homogeneous and heterogeneous nucleation is readily studied in these mixed systems.