  Benzene ice contributes to an emission feature detected by the Cassini
Composite InfraRed Spectrometer (CIRS) near 682 cm^{-1} in Titan's late
southern fall polar stratosphere. It is as well one of the dominant components
of the CIRS-observed High Altitude South Polar (HASP) ice cloud observed in
Titan's mid stratosphere during late southern fall. Titan's stratosphere
exhibits significant seasonal changes with temperatures that spatially vary
with seasons. A quantitative analysis of the chemical composition of infrared
emission spectra of Titan's stratospheric ice clouds relies on consistent and
detailed laboratory transmittance spectra obtained at numerous temperatures.
However, there is a substantial lack of experimental data on the spectroscopic
and optical properties of benzene ice and its temperature dependence,
especially at Titan-relevant stratospheric conditions. We have therefore
analyzed in laboratory the spectral characteristics and evolution of benzene
ice's vibrational modes at deposition temperatures ranging from 15 K to 130 K,
from the far- to mid-IR spectral region (50 - 8000 cm^{-1}). We have determined
the amorphous to crystalline phase transition of benzene ice and identified
that a complete crystallization is achieved for deposition temperatures between
120 K and 130 K. We have also measured the real and imaginary parts of the ice
complex refractive index of benzene ice from 15 K to 130 K. Our experimental
results significantly extend the current state of knowledge on the deposition
temperature dependence of benzene ice over a broad infrared spectral range, and
provide useful new data for the analysis and interpretation of Titan-observed
spectra.
