Infrared optical properties of thin H_2O, NH_3, and CO_2 cryofilms

OPTICAL CONSTANTS OF NH3AND NH3:N2AMORPHOUS ICES IN THE NEAR-INFRARED AND MID-INFRARED REGIONS

“…Pure amorphous NH 3 ices and NH 3 :N 2 mixtures grown at 15 K present a higher optical quality, as inferred from the higher contrast of the He-Ne interference pattern. On the contrary, for pure NH 3 ices deposited at 30 K, only a few interference maxima could be measured, indicating that some film fracture or scattering phenomenon takes place above ∼1 μm, as was already reported in the literature (Wood & Roux 1982). We have also noticed that due to the fast growing rates used in our experiments, ∼5 nm s −1 , the temperature stability of the ices grown at 15 K is limited to ices up 2 μm thick.…”

“…The refractive index n 0 can be estimated from the intensity ratio between the maxima and the minima of the interference pattern collected by the photodiode (Goodman 1978). For amorphous NH 3 ice, there are some n 0 values given in the literature that range from 1.37 (Wood & Roux 1982; 20 K) to 1.44 (Dawes et al 2007;25 K). From our experiments for pure NH 3 ices at 15 K and 30 K, we estimated n 0 values of 1.36 ± 0.01 and 1.38 ± 0.01, respectively, and 1.26 ± 0.01 for the NH 3 :N 2 (1:1.7) mixture at 15 K. As far as we know, no previous n 0 values have been published for NH 3 :N 2 mixtures.…”

“…In order to determine the complex refractive index N f = n−ik of thin solid films from normal incidence IR transmittance measurements, we used an analytical model of a three layer film-window-film transmission, based on the Fresnel equations, similar to that employed by Wood & Roux (1982), Toon et al (1994), andFernández-Torre et al (2005). This model is presented in Appendix A.…”

“…A good, current compilation of the investigations conducted on NH 3 optical constants is presented in Howett et al (2007). For the amorphous phase of NH 3 , the most complete results, as far as we know, are those of Wood & Roux (1982). These authors reported optical constants of NH 3 at 20 K for the 2.7-20 μm spectral range.…”

Thermal desorption of CH4 retained in CO2 ice

“…CO 2 has been studied from several points of view: Its optical constants (n, k); integrated absorption coefficient (A); spectral properties before and after UV photolysis and ion irradiation, using infrared spectroscopy, and density have been widely derived in previous works (Wood & Roux 1982;Hudgins et al 1993;Ehrenfreund et al 1997;Baratta et al 1998).…”