The influence of particle shapes and sizes in the CO ice stretching mode

R Vilaplana,F Moreno-Danvila,D Guirado,J Canto

doi:10.5047/eps.2009.07.001

R Vilaplana, F Moreno-Danvila + Show 2 more

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https://doi.org/10.5047/eps.2009.07.001

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Abstract

Ices are major components of dust grains in the interstellar medium, with H2O, CO, and CO2 ices being the most ubiquitous. We have studied the influence of particle shapes and sizes on the profile of the CO ice stretching mode by means of computational calculations. The extinction factors were calculated using Mie and DDA codes for a number of shapes and size parameters, ranging from the Rayleigh regime up to 3. A scattering peak displaced towards the reddish wavelength for size parameters larger than 1 was observed in all cases considered, independently of the ice (CO and CO2), the shapes (sphere, spheroid with axial proportion 5, DW1999, and aggregates), and the inclusion of other constituents, such as silicate. We have attributed this fact to the grain growth. Certain shapes also produced a double-peaked profile but in the wavelength range in which the surface modes can be observed. The calculations, including those for silicate, show a decrease in the band strength but the changes in the stretching mode profile of CO ice are not significant.

Highlights

Ices are major components of dust grains, influencing the chemical and physical processes in the interstellar medium (ISM)
We have studied the influence of particle shapes and sizes on the profile of the CO ice stretching mode by means of computational calculations
As starting point, we have mainly considered the influence of the external shape of the dust grains on the CO ice stretching mode

Summary

Introduction

Ices are major components of dust grains, influencing the chemical and physical processes in the interstellar medium (ISM). In this field, spectroscopic methods play a crucial role. Infrared (IR) observations of some of their main bands show different profiles depending on the line of sight These profiles and their positions can be influenced by different factors, such as the molecular environment (Hudgins et al, 1993; Ehrenfreund et al, 1996), the temperature (Schmitt et al, 1989; Smith et al, 1994; Raut et al, 2004), the irradiation history (Palumbo, 2006; Fama et al, 2008), and the particle shapes and sizes (Dartois et al, 2003; Dartois, 2006). We have focused our attention on the stretching mode of CO ice

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