FREQUENCY-DEPENDENT OPTICAL-CONSTANTS OF WATER ICE OBTAINED DIRECTLY FROM AEROSOL EXTINCTION SPECTRA

We report here a new approach for determining frequency-dependent real and imaginary components of the refractive index of crystalline solid s directly from the observation of the infrared spectra of the corresp onding aerosols. The interplay between scattering and absorption obser ved in large (>0.5-mu m-radius) particles allows us to properly scale the imaginary component, determined from the absorption spectrum of sm all (around 0.3-mu m-radius) aerosols, using calculations based on the Mie scattering theory. Once the imaginary indices are Properly scaled , the corresponding real indices are determined through a Kramers-Kron ig analysis. The method is applied to the study of water ice aerosols, and comparisons with previous measurements confirm that the method is sound and accurate. Reported here is a detailed study of the temperat ure dependence of the refractive index of ice. Experiments are reporte d over the temperature range from 130 to 210 K, which includes the reg ion of interest for the study of polar stratospheric clouds (PSC's).