Infrared spectra and optical constants of astronomical ices: IV. Benzene and pyridine

Abstract

Infrared (IR) spectra of two solid aromatic compounds, benzene (C6H6) and pyridine (C5H5N), have been recorded in their amorphous and crystalline states. Measurements of density and refractive index (λ = 670 nm) are reported for each form of each compound, quantities needed to compute IR intensities and optical constants for use in laboratory experiments and astronomical observations. These are the first such measurements of each compound's density, refractive index, and spectra at temperatures relevant to the outer solar system and interstellar medium, with all measurements being made in a single laboratory. We have used these results to determine both IR band strengths and optical constants for benzene and pyridine ices in amorphous and crystalline forms. Also, the intensity of benzene's IR absorbance near 1477 cm−1 is measured in samples containing H2O-ice and compared to the strength of the same band in anhydrous amorphous benzene, the first comparison of this type for this compound. Suggestions are made for applications and future work related to the chemistry of icy bodies in the Solar System and the interstellar medium.