Variation of Single Particle Mid-Infrared Emission Spectrum with Particle Size

The emission spectra of single particles of inorganic solids as a function of particle size have been recorded from 6 micro to 11.8 micro. For small optically thin particles, an emission maximum is produced in the reststrahlen region. The emission behavior is dominated by scattering and can be adequately described in terms of Mie absorption efficiency factors. As the particle size is increased, the emission band reverses its polarity, and the spectrum approaches that of a polished plate. The data provide source functions necessary for determining the emission behavior of particulate samples in which temperature gradients exist, such as on the lunar surface. The data are of particular interest for interpreting the spectral behavior of circumstellar silicate particles.