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The unidentified interstellar infrared bands: PAHs as carriers?
S Schlemmer1, D J Cook, J A Harrison
1Department of Chemistry, University of California, Berkeley 94720-1460, USA.
Science (New York, N.Y.)
|September 16, 1994
Summary
Laboratory infrared spectra of naphthalene and pyrene do not match astronomical observations. This suggests small polycyclic aromatic hydrocarbons are not responsible for unidentified infrared emission bands in space.
Area of Science:
- Astrochemistry
- Spectroscopy
Background:
- Astronomical objects exhibit unidentified infrared emission bands.
- Polycyclic Aromatic Hydrocarbons (PAHs) are potential carriers of these bands.
- Naphthalene and pyrene are representative small, unsubstituted PAHs.
Purpose of the Study:
- To measure the infrared emission spectra of gas-phase naphthalene and pyrene.
- To compare laboratory spectra with astronomical observations of unidentified infrared emission bands.
- To determine if small, unsubstituted PAHs can explain the astronomical observations.
Main Methods:
- Infrared emission spectra were measured for gas-phase naphthalene and pyrene.
- Measurements were conducted in the 3 to 7.5 micrometer range.
- Ultraviolet laser desorption-excitation and single-photon counting infrared spectroscopy were employed.
Main Results:
- Significant discrepancies were observed between laboratory spectra and astronomical data.
- Wavelengths and relative intensities of spectral features did not match.
- Laboratory emission spectra of naphthalene and pyrene did not replicate the observed astronomical bands.
Conclusions:
- Small, neutral, unsubstituted polycyclic aromatic hydrocarbons are unlikely carriers of the unidentified infrared emission bands.
- The origin of unidentified infrared emission bands in astronomical objects remains unknown.
- Further research is needed to identify the molecules responsible for these spectral features.
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