An Infrared Spectroscopic Study of Amorphous and Crystalline Ices of Vinylacetylene and Implications for Saturn's Satellite Titan

Abstract

Laboratory infrared spectra of amorphous and crystalline vinylacetylene ices were recorded in the range of 7000-400 cm^-1. The spectra showed several amorphous features in the ice deposited at 10 K, which were then utilized to monitor a phase transition between 93 ± 1 K to form the crystalline structure. Successive heating allows monitoring of the sublimation profile of the vinylacetylene sample in the range of 101-120 K. Considering Titan's surface temperature of 94 K, vinylacetylene ice is likely to be crystalline. Analogous studies on related planetary-bound molecules such as triaceylene and cyanoacetylene may be further warranted to gain better perspectives into the composition of the condensed phases in the Titan's atmosphere (aerosol particles) and of Titan's surface. Based on our studies, we recommend utilizing the ν₁ and ν₁₆//ν₁₁/ν₁₇ fundamentals at about 3300 and 650 cm^-1 to determine if solid vinylacetylene is crystalline or amorphous on Titan.