2006ApJ...642..966D

Infrared spectra of long-chain n-alkane molecules, CH₃(CH₂)_m_CH3_, with m>8, have been obtained in absorption and emission and are compared to spectra of a variety of interstellar sources. Absorption spectra of these molecules in the 3.4 µm region are remarkably similar, consisting of narrow features at 3.384, 3.425, and 3.508 µm, independent of chain length. These features are not seen in absorption in interstellar clouds. We estimate that the column density of CH₂groups in long-chain n-alkanes is typically N<(1.2-2.9)x10¹⁶/cm2 in VI Cyg 12. Given the narrow width of these features, this limit could be improved with higher resolution observations. Thermal spectra of these molecules show a number of characteristic features near 6.8, 7.3, and 13.9 µm that should be useful in determining whether large n-alkane molecules are present in interstellar emission sources.