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Infrared Spectroscopy of Polycyclic Aromatic Hydrocarbon CationsIn spite of the fact that the infrared spectroscopic properties of only a few isolated ionized polycyclic aromatic hydrocarbons (PAHs) are known, gaseous, ionized PAHs are thought to be responsible for a very common family of infrared interstellar emission bands. In order to provide a data base to test this hypothesis and, if borne out, to use this emission band family as a probe of many different interstellar environments, we are carrying out a thorough study of the infrared spectroscopic properties of neutral and ionized PAHs in argon matrices. Here we present the near and mid-infrared spectra of the cations of the five most thermodynamically favored PAHs up to coronene: phenanthrene, pyrene, benzo[e]pyrene, benzo[ghilperylene, and coronene. The properties of naphthalene, the first member of the series, are given elsewhere. The spectra of perdeuterated phenanthrene and pyrene are also reported. For those molecules which have been previously studied (pyrene, d(10)-pyrene, and coronene), band positions and relative intensities are in agreement. In all cases we report additional features. Absolute integrated absorbance values are given for the phenanthrene, perdeutero-phenanthrene, pyrene, benzo[ghi]perylene, and coronene cations. With the exception of coronene,the cation bands corresponding to the CC modes are typically 2-5 times more intense than those of the CH out-of-plane bending vibrations. For the cations the CC stretching and CH in-plane bending modes give rise to bands which are an order of magnitude stronger than for the neutral species, and the CH out-of-plane bends produce bands which are 5-20 times weaker than in the neutral species. This behavior is similar to that found in most other PAH cations studied to date. The astronomical implications of these PAH cation spectra are also discussed.
Document ID
20020006175
Acquisition Source
Ames Research Center
Document Type
Preprint (Draft being sent to journal)
Authors
Hudgins, D. M.
(NASA Ames Research Center Moffett Field, CA United States)
Allamandola, L. J.
(NASA Ames Research Center Moffett Field, CA United States)
Wittebon, Fred C.
Date Acquired
August 20, 2013
Publication Date
January 1, 1994
Subject Category
Chemistry And Materials (General)
Funding Number(s)
PROJECT: RTOP 188-44-57-01
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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