The comparison of infrared (IR) spectra of laboratory materials with the telescopic spectra of astronomical objects has proven to be a very powerful technique for the identification of materials in space. Materials so far identified include silicate grains, microdiamonds, and mixed-molecular ices.

The figure below shows an example of the comparison between the spectrum of a newly forming star (W33A) and the absorption bands of a number of different laboratory analog materials. Click on the picture to obtain an even larger image.

The full IR spectrum of the protostar is in the upper left of the figure. The solid line represents the expected blackbody energy distribution being emitted by the star and the points respresent the spectrum that was actually measured telescope. To learn more about how this is done follow this link. The large absorption bands superimposed on the blackbody curve are produced by materials along the line-of-sight between us and the protostar, which absorb light at characteristic frequencies defined by their molecular structure. The other portions of figure show examples of spectral matches of the observed absorption bands in the spectrum of W33A to the bands produced by various ice phase molecules measured in the laboratory. For example, the matches in the upper right portion of the figure demonstrate that the features near 6.0 and 6.8 µm can be explained by the presence of ices containing H₂O (water), CH₃OH (methanol). The lower left shows a fit to another methanol ice band and the 2880 cm^-1 band due to microdiamonds. The spectra in the lower right demonstrate the presence of CO-containing ices and "XCN".

Studies of this type identified or tentatively identified compounds such as: H₂O (water), CH₃OH (methanol), CH₄ (methane), CO (carbon monoxide), CO₂ (carbon dioxide), H₂C=O (formaldehyde), HCO (formyl radical), "XCN" (probably some form of nitrile or isonitrile), polycyclic aromatic hydrocarbons (PAHs). In ice mantles where water is less prevalent there may also be abundant N₂, O₂, and H₂.

Bernstein, M. P., & Sandford, S. A. (1999). Variations in the Strength of the Infrared Forbidden 2328.2 cm-1 Fundamental of Solid N₂ in Binary Mixtures. Spectrochimica Acta A, 55 pp. 2455-2466. Read the abstract.

Lacy, J. H., Faraji, H., Sandford, S. A., & Allamandola, L. J. (1998). Unraveling the 10 µm 'Silicate' Feature of Protostars: The Detection of Frozen Interstellar Ammonia. Astrophys. J. (Letters) 501, L105-L109.

Elsila, J., Allamandola, L. J., and Sandford, S. A. (1997). The 2140 cm-1 (4.673 µm) Solid CO Band: The Case for Interstellar O₂ and N₂ and the Photochemistry of Non-Polar Interstellar Ice Analogs. Astrophys. J. 479, 818-838.

Bernstein, M. P., Sandford, S. A., & Allamandola, L. J. (1997). The Infrared Spectra of Nitriles and Related Compounds Frozen in Ar and H₂O. Astrophys. J. 476, 932-942.

Sandford, S. A. (1996). The Inventory of Interstellar Materials Available for the Formation of the Solar System. Meteoritics and Planetary Science 31, 449-476.

Sandford, S. A. (1996). The Composition of Interstellar Grains and Ices. In Polarimetry of the Interstellar Medium, eds. W. Roberge & D. C. B. Whittet, (Astron. Soc. Pac. Conf. Series, Vol. 97: San Francisco), pp. 29-47.

Sandford, S. A., Allamandola, L. J., & Geballe, T. R. (1993). Spectroscopic Detection of Molecular Hydrogen Frozen in Interstellar Ices. Science 262, 400-402.

Tegler, S. C., Weintraub, D. A., Allamandola, L. J., Sandford, S. A., Rettig, T. W., & Campins, H. (1993). Detection of the 2165 cm-1 (4.619 µm) XCN Band in the Spectrum of L1551 IRS 5. Astrophys. J. 411, 260-265.

Sandford, S. A., & Allamandola, L. J. (1993). H₂ in Interstellar and Extragalactic Ices: Infrared Characteristics, UV Production, and Implications. Astrophys. J. (Letters) 409, L65-L68.

Allamandola, L. J., Sandford, S. A., Tielens, A. G. G. M., & Herbst, T. M. (1993). "Diamonds" in Dense Molecular Clouds: A Challenge to the Standard Interstellar Paradigm. Science 260, 64-66.

Allamandola, L. J., Sandford, S. A., Tielens, A. G. G. M., & Herbst, T. M. (1992). Spectroscopy of Dense Clouds in the C-H Stretching Region: Methanol and "Diamonds". Astrophys. J. 399, 134-146.

Schutte, W. A., Tielens, A. G. G. M., & Sandford, S. A. (1991). 10 µm Spectra of Protostars and the Solid Methanol Abundance. Astrophys. J. 382, 523-529.

Sandford, S. A., & Allamandola, L. J. (1990). The Physical and Infrared Spectral Properties of CO₂ in Astrophysical Ice Analogs. Astrophys. J. 355, 357-372.

Allamandola, L. J., & Sandford, S. A. (1988). Laboratory simulation of dust spectra. In Dust in the Universe, (M.E. Bailey & D.A. Williams, eds.), Cambridge Univ. Press: Cambridge, pp. 229-263.

Sandford, S. A., Allamandola, L. J., Tielens, A. G. G. M., & Valero, G. (1988). Laboratory studies of the infrared spectral properties of CO in astrophysical ices. Astrophys. J. 329, 498-510.