A temperature study of methanol interstellar ice analogues

Abstract

Methanol ice has been studied in the field of astrochemistry for many years. As a simple organic compound, CH3OH is extremely interesting in the study of ice formation and evolution. There are three forms of methanol ice – amorphous, α-crystalline, and β-crystalline. Although there are studies focused on the comparison of crystalline and amorphous phases in terms of chemical properties, there is a lack of systematic studies on phase transition. Factors such as pressure, temperature, and rate of ice formation have an influence on the process of phase transition. In this study, the influence of temperature on the vibrational properties of methanol ice is considered. For the experimental section, a Portable Astrochemistry Chamber (PAC) with the ability to control deposition pressure and temperature was used. The temperature of phase transition was experimentally determined at 103 K and for analysis of the ice structure, two vibrational modes were chosen – OH stretch and CH3 in-plane rocking. Moreover, depositions at higher temperatures were performed with the result of different vibrational properties depending on ice formation conditions. This study presents the temperature-dependant properties of methanol ice in the mid-infrared spectrum and considers the possibility of thermal history determination.