CO Cocktails: Stirred... But Not Shaken

Abstract

Dust grains in molecular clouds are covered by ice mantles composed of complex “cocktail mixtures” of molecules frozen onto the grains (e.g. Schutte 1996). Solid CO in the ice mantles is identified by an absorption feature at 4.67μm, corresponding to the stretch of the CO molecule. The observed features generally show two components: a narrow dominant one corresponding to CO in a nonpolar or weakly polar mixture, and a broader one appearing as a long-wavelength wing corresponding to CO in a polar mixture (Tielens et al. 1991, Kerr et al. 1993, Chiar et al. 1995, Teixeira et al. 1998). The comparison of the observed CO-ice bands with laboratory astrophysical ice analogs might be used as a probe of the astrophysical conditions in the coolest regions of the cloud.