IR Optical Constants of solid CO and CO2
G.A. Baratta and M.E. Palumbo, JOSA A, 15, 3076-3085, 1998

Optical constants of  CO and CO2 ices deposited at 12.5 K have been derived in the infrared spectral range 4200-500 cm-1 (2.3-20 micrometers) with the resolution of 2 cm-1, at the Experimental Astrophysical Laboratory of the  Catania Astrophysical Observatory . Icy film were accreted on a silicon substrate inclined of 45 degree with respect to the infrared beam of the spectrometer. The reliability of the derived optical constants greatly depends on the precision to which  the film thickness is measured. In our experimental set up, a He-Ne laser is used to monitor the thickness during accretion by looking at its interference pattern. After the reflection from the substrate, the laser beam follows the same path of the infrared beam and can be detected by the pyro-detector of the infrared spectrometer.
 

The refractive index of the ice at the laser wavelength must be known in order to measure the thickness. In our method of computation the refractive index of the film is derived from the amplitude of the interference curve.
Transmittance spectra were taken at different thicknesses (0.05-3 micrometers) with the electric vector parallel (p polarized) and perpendicular (s polarized) to the incidence plane. Optical constants have been derived, using a non-linear least squares method, in such a way they satisfy the Kramers-Kronig relation and give the best agreement with the transmittance spectra at oblique incidence  for p and s polarizations measured at different thicknesses. This procedure can clearly seperate the contribution of n and k to the spectrum. The experimental set-up, the method of computation and the theoretical model are described in detail in the following article:
G.A. Baratta and M.E. Palumbo, Infrared optical constants of CO and CO2 thin icy films, JOSA A, 15, 3076-3085, 1998. Please refer to this article when using datafiles from this page.


 click here to get the optical constants of CO2



 click here to get the optical constants of CO

Back to the OACT home page