Browsing by Author "Allamandola, Louis"

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Infrared spectra of ovalene (C32H14) and hydrogenated ovalene (C32H15 center dot) in solid para-hydrogen
(2016-11-07)
Tsuge, Masashi
;
Bahou, Mohammed
;
Wu, Yu-Jong
;
Allamandola, Louis
;
Lee, Yuan-Pern
We report the infrared (IR) spectra of ovalene (C32H14) and hydrogenated ovalene (C32H15 center dot) in solid para-hydrogen (p-H-2). The hydrogenated ovalene and protonated ovalene were generated from electron bombardment of a mixture of ovalene and p-H-2 during deposition of a matrix at 3.2 K. The features that decreased with time have been previously assigned to 7-C32H15+, the most stable isomer of protonated ovalene (Astrophys. J., 2016, 825, 96). The spectral features that increased with time are assigned to the most stable isomer of hydrogenated ovalene (7-C32H15 center dot) based on the expected chemistry and on a comparison with the vibrational wavenumbers and IR intensities predicted by the B3PW91/6-311++ G(2d, 2p) method. The mechanism of formation of 7-C32H15 center dot is discussed according to the observed changes in intensity and calculated energetics of possible reactions of H + C32H14 and isomerization of C32H15 center dot. The formation of 7-C32H15 center dot is dominated by the reaction H + C32H14 -> 7-C32H15 center dot, implying that, regardless of the presence of a barrier, the hydrogenation of polycyclic aromatic hydrocarbons occurs even at 3.2 K.
THE INFRARED SPECTRUM OF PROTONATED OVALENE IN SOLID PARA-HYDROGEN AND ITS POSSIBLE CONTRIBUTION TO INTERSTELLAR UNIDENTIFIED INFRARED EMISSION
(2016-07-10)
Tsuge, Masashi
;
Bahou, Mohammed
;
Wu, Yu-Jong
;
Allamandola, Louis
;
Lee, Yuan-Pern
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-H-2) matrix at 3.2 K, generated by bombarding a mixture of ovalene and p-H-2 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.