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Letter to the Editor
New PAH mode at 16.4 µm *
C. Moutou 1,
L. Verstraete 2,
A. Léger 2,
K. Sellgren 3 and
W. Schmidt 4
Received 12 October 1999 / Accepted 23 December 1999
The detection of a new 16.4 µm emission feature in the ISO-SWS spectra of NGC 7023, M17, and the Orion Bar is reported. Previous laboratory experiments measured a mode near this wavelength in spectra of PAHs (Polycyclic Aromatic Hydrocarbons), and so we suggest the new interstellar 16.4 µm feature could be assigned to low-frequency vibrations of PAHs. The best carrier candidates seem to be PAH molecules containing pentagonal rings.
Key words: ISM: abundances ISM: dust, extinction ISM: reflection nebulae
* based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: the United Kingdom, France, the Netherlands, Germany), and with the participation of ISAS and NASA.
Send offprint requests to: C. Moutou