The infrared spectrum of protonated ovalene in solid para-hydrogen and its possible contribution to interstellar unidentified infrared emission

Masashi Tsuge, Mohammed Bahou, Yu Jong Wu, Louis Allamandola, Yuan-Pern Lee

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15 Scopus citations

Abstract

The mid-infrared emission from galactic objects, including reflection nebulae, planetary nebulae, proto-planetary nebulae, molecular clouds, etc, as well as external galaxies, is dominated by the unidentified infrared (UIR) emission bands. Large protonated polycyclic aromatic hydrocarbons (H+PAHs) were proposed as possible carriers, but no spectrum of an H+PAH has been shown to exactly match the UIR bands. Here, we report the IR spectrum of protonated ovalene (7-C32H15 +) measured in a para-hydrogen (p-H2) matrix at 3.2 K, generated by bombarding a mixture of ovalene and p-H2 with electrons during matrix deposition. Spectral assignments were made based on the expected chemistry and on the spectra simulated with the wavenumbers and infrared intensities predicted with the B3PW91/6-311++G(2d,2p) method. The close resemblance of the observed spectral pattern to that of the UIR bands suggests that protonated ovalene may contribute to the UIR emission, particularly from objects that emit Class A spectra, such as the IRIS reflection nebula, NGC 7023.

Original languageEnglish
Article number96
JournalAstrophysical Journal
Volume825
Issue number2
DOIs
StatePublished - 10 Jul 2016

Keywords

  • ISM: lines and bands
  • ISM: molecules
  • astrochemistry
  • infrared: ISM

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