Publication
Reference
Sandford Scott A., Allamandola Louis J. (1993). Condensation and Vaporization Studies of CH 3OH and NH 3 Ices: Major Implications for Astrochemistry. Astrophys. J., 417, 815 - 825.
Names
  • Scott A. Sandford
  • Louis J. Allamandola
Article and keywords
Title
Condensation and Vaporization Studies of CH 3OH and NH 3 Ices: Major Implications for Astrochemistry
Abstract
In an extension of previously reported work on ices containing H2O, CO, CO2, SO2, H2S, and H2, we present measurements of the physical and infrared spectral properties of ices containing CH3OH and NH3. The condensation and sublimation behavior of these ice systems is discussed and surface binding energies are presented for all of these molecules. The surface binding energies can be used to calculate the residence times of the molecules on grain surfaces as a function of temperature. It is demonstrated that many of the molecules used to generate radio maps of and probe conditions in dense clouds, for example CO and NH3, will be significantly depleted from the gas phase by condensation onto dust grains. Attempts to derive total column densities solely from radio maps that do not take condensation effects into account may vastly underestimate the true column densities of any given species. Simple CO condensation onto and vaporization off of grains appears to be capable of explaining the observed depletion of gas phase CO in cold, dense molecular cores. This is not the case for NH3, however, where thermal considerations alone predict that all of the NH3 should be condensed onto grains. The fact that some gas phase NH3 is observed indicates that additional desorption processes must be involved. The surface binding energies of CH3OH, in conjunction with this molecule's observed behavior during warm up in H2O-rich ices, is shown to provide an explanation of the large excess of CH3OH seen in many warm, dense molecular cores. The near-infrared spectrum and associated integrated band strengths of CH3OH- containing ice are given, as are middle infrared absorption band strengths for both CH3OH and NH3.
Keywords
spectroscopy, transmission spectra, band position, band vibration mode, mid-IR, Condensation, Sublimation, molecular solid, molecular liquid, CH3OH, NH3, ices, CO, Ammonia, Methyl Alcohol, Carbon Monoxide, Astrophysics, Cosmochemistry
Content
spectral data, band list data, astrophysics
Year
1993
Journal
The Astrophysical Journal
Volume
417
Pages
815 - 825
Pages number
11
Document type
article
Publication state
published
Doi
10.1086/173362
Identifiers