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The relation between ices in the envelopes and disks surrounding YSOs andthose in the quiescent interstellar medium is investigated. For a sample of 31stars behind isolated dense cores, ground-based and Spitzer spectra andphotometry in the 1-25 um wavelength range are combined. The baseline for thebroad and overlapping ice features is modeled, using calculated spectra ofgiants, H2O ice and silicates. The adopted extinction curve is derivedempirically. Its high resolution allows for the separation of continuum andfeature extinction. The extinction between 13-25 um is ~50% relative to that at2.2 um. The strengths of the 6.0 and 6.85 um absorption bands are in line withthose of YSOs. Thus, their carriers, which, besides H2O and CH3OH, may includeNH4+, HCOOH, H2CO and NH3, are readily formed in the dense core phase, beforestars form. The 3.53 um C-H stretching mode of solid CH3OH was discovered. TheCH3OH/H2O abundance ratios of 5-12% are larger than upper limits in the Taurusmolecular cloud. The initial ice composition, before star formation occurs,therefore depends on the environment. Signs of thermal and energetic processingthat were found toward some YSOs are absent in the ices toward backgroundstars. Finally, the peak optical depth of the 9.7 um band of silicates relativeto the continuum extinction at 2.2 um is significantly shallower than in thediffuse interstellar medium. This extends the results of Chiar et al. (2007) toa larger sample and higher extinctions.

Ice and Dust in the Quiescent Medium of Isolated Dense Cores