PAHs are a class of very stable organic molecules made up of only carbon and hydrogen. These molecules are flat, with each carbon having three neighboring atoms much like graphite. At right is a space filling representation of the PAH coronene (C₂₄H₁₂). The structures of a variety of representative PAHs can be seen here. These molecules are highly carcinogenic but they are also very common. They are a standard product of combustion from automobiles and airplanes and some (such as benzo[a]pyrene) are present in charcoal broiled hamburgers.

Here is a comparison of an infrared spectrum of a distant object with the raman spectrum of auto soot. We do not claim that they have alot of cars out there but that the high temperatures present lead to the same kinds of molecules that we see in auto engines. PAHs are now commonly thought to be the carriers of the "unidentified" infrared bands (UIRs) and We now believe that PAHs or PAH cations (a PAH with an electron missing) are also the best candidates for the diffuse interstellar bands (DIBs).

Chemists often ask us "where do you get all of these pure PAHs?"

For more detailed information on our laboratory work on PAHs, see:

The Infrared Spectra of PAHs

Allamandola, L. J., Hudgins, D. M., & Sandford, S. A. (1999). Modeling the Unidentified Infrared Emission with Combinations of Polycyclic Aromatic Hydrocarbons. Astrophys. J. (Letters) 511, L115-L119.

Langhoff, S. R., Bauschlicher, Jr., C. W., Hudgins, D. M., Sandford, S. A., & Allamandola, L. J. (1998). Infrared spectra of substituted polycyclic aromatic hydrocarbons. J. Phys. Chem. A 102, 1632-1646.

Hudgins, D. M., & Sandford, S. A. (1998a). Infrared Spectroscopy of Matrix-Isolated Polycyclic Aromatic Hydrocarbons 1. PAHs Containing 2 to 4 Rings. J. Phys. Chem. 102, 329-343.

Hudgins, D. M., & Sandford, S. A. (1998b). Infrared Spectroscopy of Matrix-Isolated Polycyclic Aromatic Hydrocarbons 2. PAHs Containing 5 or More Rings. J. Phys. Chem. 102, 344-352.

Hudgins, D. M., & Sandford, S. A. (1998c). Infrared Spectroscopy of Matrix-Isolated Polycyclic Aromatic Hydrocarbons 3. Fluoranthene and the Benzofluoranthenes. J. Phys. Chem. 102, 353-360.

Bauschlicher, Jr., C. W., Langhoff, S. R., Sandford, S. A., & Hudgins, D. M. (1997). Infrared Spectra of Perdeuterated Naphthalene, Phenanthrene, Chrysene, and Pyrene. J. Phys. Chem. A 101, #13, 2414-2422.

Hudgins, D. M., Sandford, S. A., & Allamandola, L. J. (1994). Infrared Spectroscopy of Polycyclic Aromatic Hydrocarbon Cations I: Matrix-Isolated Naphthalene and Perdeuterated Naphthalene. J. Phys. Chem. 98, 4243-4253.

Witteborn, F. C., Sandford, S. A., Bregman, J. D., Allamandola, L. J., Cohen, M., & Wooden, D. (1989). New Emission Features in the 11-13 µm Region and Their Relationship to Polycyclic Aromatic Hydrocarbons. Astrophys. J. 341, 270-277.

The Chemistry of PAHs and PAHs in Extraterrestrial Materials

Bernstein, M. P., Sandford, S. A., Allamandola, L. J., Gillette, J. S., Clemett, S. J., & Zare, R. N. (1999). UV Irradiation of Polycyclic Aromatic Hydrocarbons in Ices: Production of Alcohols, Quinones, and Ethers. Science 283, 1135-1138.

Allamandola, L. J., Sandford, S. A., & Wopenka, B. (1987). Interstellar polycyclic aromatic hydrocarbons and carbon in interplanetary dust particles and meteorites. Science 237, 56-59.

The Ultraviolet/Visible Spectra of PAHs

Salama, F. (1999). Polycyclic Aromatic Hydrocarbons in the Interstellar Medium. A Review. In Solid Interstellar Matter: The ISO Revolution, L. d'Hendecourt, C. Joblin & A. Jones, eds., EDP Sciences, (Springer-Verlag: Les Ulis), pp. 65-87.

Romanini, D., Biennier, L., Salama, F., Kachanov, A., Allamandola, L. J., & Stoeckel, F. (1999). Jet-discharge cavity ring down spectroscopy of ionized polycyclic aromatic hydrocarbons: Progress in testing the PAH hypothesis for the diffuse interstellar band problem. Chem. Phys. Letters 303, 165-170.

Joblin, C., Salama, F., & Allamandola, L. J. (1999). Absorption and emission spectroscopy of perylene (C₂₀H₁₂) isolated in Ne, Ar, and N₂ matrices. J. Chem. Phys. 110, 7287-7297.

Joblin, C., Salama, F., & Allamandola, L. J. (1995). Photoinduced Fluorescence from the Perylene Cation Isolated in Ne and Ar Matrices. J. Chem. Phys. 102, 9743-9745.

Salama, F., Joblin, C., & Allamandola, L. J. (1994). Electronic absorption spectroscopy of matrix-isolated polycyclic aromatic hydrocarbon cations. II. The phenanthrene cation (C₁₄H₁₀+) and its 1-Methyl derivative. J. Chem. Phys. 101, 10252-10262.

Du, P., Salama, F., & Loew, G. H. (1993). Theoretical study on the electronic spectra of a polycyclic aromatic hydrocarbon, naphthalene, and its derivatives. Chem. Phys. 173, 421-437.

Salama, F., & Allamandola, L. J. (1991). The role of matrix material and CCl₄ (electron acceptor) on the ionization mechanisms of matrix-isolated naphthalene. J. Chem. Phys. 95, 6190-6191.

Salama, F., & Allamandola, L. J. (1991). Electronic absorption spectroscopy of matrix-isolated polycyclic aromatic hydrocarbon cations. I. The naphthalene cation (C₁₀H₈+). J. Chem. Phys. 94, 6964-6977.