Characterization of thin film CO${}_2$ ice through the infrared ${\nu }_1+{\nu }_3$ combination mode

Abstract

Carbon dioxide is abundant in ice mantles of dust grains; some is found in the pure crystalline form as inferred from the double peak splitting of the bending profile at about 650 cm${}^{-1}$. To study how CO${}_2$ segregates into the pure form from water-rich mixtures of ice mantles and how it then crystallizes, we used Reflection Absorption InfraRed Spectroscopy (RAIRS) to study the structural change of pure CO${}_2$ ice as a function of both ice thickness and temperature. We found that the ${\nu }_1+{\nu }_3$ combination mode absorption profile at 3708~cm${}^{-1}$ provides an excellent probe to quantify the degree of crystallinity in CO${}_2$ ice. We also found that between 20 and 30~K, there is an ordering transition that we attribute to reorientation of CO${}_2$ molecules, while the diffusion of CO${}_2$ becomes significant at much higher temperatures. In the formation of pure crystalline CO${}_2$ in ISM ices, the rate limiting process is the diffusion/segregation of CO${}_2$ molecules in the ice instead of the phase transition from amorphous to crystalline after clusters/islands of CO${}_2$ are formed.

8 pages, 8 figures, submitted to MNRAS

References in corpus (3)

• The c2d Spitzer spectroscopic survey of ices around low-mass young stellar objects II: CO2
• CO${}_2$ Infrared Phonon Modes in Interstellar Ice Mixtures
• Diffusion and Clustering of Carbon Dioxide on non-porous Amorphous Solid Water

Cited by in corpus (6)

• Transmission Electron Microscopy Study of the Morphology of Ices Composed of H2O, CO2, and CO on Refractory Grains
• The Effective Surface Area of Amorphous Solid Water Measured by the Infrared Absorption of Carbon Monoxide
• Mid-IR and VUV Spectroscopic Characterisation of Thermally Processed and Electron Irradiated CO2 Astrophysical Ice Analogues
• Spectroscopic measurements of CH${}_3$OH in layered and mixed interstellar ice analogues
• Electron-stimulated desorption from molecular ices in the sub-keV regime
• Broadband spectroscopy of astrophysical ice analogues: II. Optical constants of CO and CO${}_2$ ices in the terahertz and infrared ranges