Optical constants of ammonium hydrosulfide ice and ammonia ice

Thin-film transmission spectra of ammonium hydrosulfide (NH4SH) ice and ammonia (NH3) ice between 1300 and 12,000 cm-1 were used to determine the ice's optical constants. The films were grown on a sapphire substrate, and a Fourier-transform spectrometer and a grating spectrometer were used together to record the spectra. Lambert's law was used to directly determine the imaginary component of the complex refractive indices; from this, the real component was derived using the Kramers-Kronig algorithm. It is shown that, contrary to what is expected, the optical constants determined for NH3 ice at 80 K are in good agreement with those in the cubic phase, rather than the metastable one. The phase of the NH4SH ice was observed to change from amorphous to polycrystalline as the film was annealed to 160 K. © 2006 Optical Society of America