scholarly journals The Interpretation of Absorption Spectra of Condensed Polycyclic Aromatic Hydrocarbons by Using a Simple Resonance Theory. I. The Resonance Structure of the Excited State in Correlation with Platt’s Theory

1963 ◽  
Vol 36 (3) ◽  
pp. 235-247 ◽  
Author(s):  
Takashi Handa
Keyword(s):  
Polycyclic Aromatic Hydrocarbons ◽  
Excited State ◽  
Absorption Spectra ◽  
Aromatic Hydrocarbons ◽  
Resonance Structure ◽  
Resonance Theory ◽  
Polycyclic Aromatic

scholarly journals High-resolution IR absorption spectroscopy of polycyclic aromatic hydrocarbons in the 3 μm region: role of hydrogenation and alkylation

2018 ◽  
Vol 610 ◽  
pp. A65 ◽  
Author(s):  
Elena Maltseva ◽  
Cameron J. Mackie ◽  
Alessandra Candian ◽  
Annemieke Petrignani ◽  
Xinchuan Huang ◽  
...  
Keyword(s):  
Polycyclic Aromatic Hydrocarbons ◽  
High Resolution ◽  
Absorption Spectra ◽  
Aromatic Hydrocarbons ◽  
Dominant Role ◽  
Selective Absorption ◽  
Ir Absorption ◽  
Spectroscopic Techniques ◽  
High Resolution Data ◽  
Polycyclic Aromatic

Aim. We aim to elucidate the spectral changes in the 3 μm region that result from chemical changes in the molecular periphery of polycyclic aromatic hydrocarbons (PAHs) with extra hydrogens (H-PAHs) and methyl groups (Me-PAHs). Methods. Advanced laser spectroscopic techniques combined with mass spectrometry were applied on supersonically cooled 1,2,3,4-tetrahydronaphthalene, 9,10-dihydroanthracene, 9,10-dihydrophenanthrene, 1,2,3,6,7,8-hexahydropyrene, 9-methylanthracene, and 9,10-dimethylanthracene, allowing us to record mass-selective and conformationally selective absorption spectra of the aromatic, aliphatic, and alkyl CH-stretches in the 3.175 − 3.636 µm region with laser-limited resolution. We compared the experimental absorption spectra with standard harmonic calculations and with second-order vibrational perturbation theory anharmonic calculations that use the SPECTRO program for treating resonances. Results. We show that anharmonicity plays an important if not dominant role, affecting not only aromatic, but also aliphatic and alkyl CH-stretch vibrations. The experimental high-resolution data lead to the conclusion that the variation in Me- and H-PAHs composition might well account for the observed variations in the 3 μm emission spectra of carbon-rich and star-forming regions. Our laboratory studies also suggest that heavily hydrogenated PAHs form a significant fraction of the carriers of IR emission in regions in which an anomalously strong 3 μm plateau is observed.

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