HIGH-RESOLUTION IR ABSORPTION SPECTROSCOPY OF POLYCYCLIC AROMATIC HYDROCARBONS: THE REALM OF ANHARMONICITY

Journal Article · Fri Nov 20 00:00:00 EST 2015 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/814/1/23· OSTI ID:22521405

Maltseva, Elena; Buma, Wybren Jan ^[1]; Petrignani, Annemieke; Candian, Alessandra; Mackie, Cameron J.; Huang, Xinchuan; Lee, Timothy J. ^[2]; Oomens, Jos ^[3]

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1. University of Amsterdam, Science Park 904, 1098 XH Amsterdam (Netherlands)
2. SETI Institute, 189 Bernardo Avenue, Suite 100, Mountain View, CA 94043 (United States)
3. Radboud University, Toernooiveld 7, 6525 ED Nijmegen (Netherlands)

We report on an experimental and theoretical investigation of the importance of anharmonicity in the 3-μm CH stretching region of polycyclic aromatic hydrocarbon (PAH) molecules. We present mass-resolved, high-resolution spectra of the gas-phase cold (∼4 K) linear PAH molecules naphthalene, anthracene, and tetracene. The measured IR spectra show a surprisingly high number of strong vibrational bands. For naphthalene, the observed bands are well separated and limited by the rotational contour, revealing the band symmetries. Comparisons are made to the harmonic and anharmonic approaches of the widely used Gaussian software. We also present calculated spectra of these acenes using the computational program SPECTRO, providing anharmonic predictions with a Fermi-resonance treatment that utilizes intensity redistribution. We demonstrate that the anharmonicity of the investigated acenes is strong, dominated by Fermi resonances between the fundamental and double combination modes, with triple combination bands as possible candidates to resolve remaining discrepancies. The anharmonic spectra as calculated with SPECTRO lead to predictions of the main bands that fall within 0.5% of the experimental frequencies. The implications for the aromatic infrared bands, specifically the 3-μm band, are discussed.

• OSTI ID: 22521405
• Journal Information: Astrophysical Journal, Vol. 814, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

74 ATOMIC AND MOLECULAR PHYSICS
79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
ABSORPTION SPECTROSCOPY
ANTHRACENE
COMPARATIVE EVALUATIONS
FERMI RESONANCE
INFRARED SPECTRA
MASS
MOLECULES
NAPHTHALENE
POLYCYCLIC AROMATIC HYDROCARBONS
S CODES
SYMMETRY
TETRACENE
VIBRATIONAL STATES