Browsing by Author "Sundararajan, Pavithraa"

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Infrared spectra of protonated and hydrogenated corannulene (C20H10) and sumanene (C21H12) in solid para-hydrogen
(2018-08-19)
Sundararajan, Pavithraa
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Tsuge, Masashi
;
Lee, Yuan-Pern
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應用化學系
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Department of Applied Chemistry
Infrared spectrum of hydrogenated corannulene rim-HC20H10 isolated in solid para-hydrogen
(2019-07-28)
Sundararajan, Pavithraa
;
Tsuge, Masashi
;
Baba, Masaaki
;
Sakurai, Hidehiro
;
Lee, Yuan-Pern
Hydrogenated polycyclic aromatic hydrocarbons have been proposed to be carriers of the interstellar unidentified infrared (UIR) emission bands and the catalysts for formation of H-2; spectral characterizations of these species are hence important. We report the infrared (IR) spectrum of mono-hydrogenated corannulene (HC20H10) in solid para-hydrogen (p-H-2). In experiments of electron bombardment of a mixture of corannulene and p-H-2 during deposition of a matrix at 3.2 K, two groups of spectral lines increased with time during maintenance of the matrix in darkness after deposition. Lines in one group were assigned to the most stable isomer of hydrogenated corannulene, rim-HC20H10, according to the expected chemistry and a comparison with scaled harmonic vibrational wavenumbers and IR intensities predicted with the B3PW91/6-311++G(2d,2p) method. The lines in the other group do not agree with predicted spectra of other HC20H10 isomers and remain unassigned. Alternative hydrogenation was achieved with H atoms produced photochemically in the infrared-induced reaction Cl + H-2 (v = 1) -> H + HCl in a Cl-2/C20H10/p-H-2 matrix. With this method, only lines attributable to rim-HC20H10 were observed, indicating that hydrogenation via a quantum-mechanical tunneling mechanism produces preferably the least-energy rim-HC20H10 regardless of similar barrier heights and widths for the formation of rim-HC20H10 and hub-HC20H10. The mechanisms of formation in both experiments are discussed. The bands near 3.3 and 3.4 mu m of rim-HC20H10 agree with the UIR emission bands in position and relative intensity, but other bands do not match satisfactorily with the UIR bands.
Infrared Spectrum of Protonated Corannulene H+C20H10 in Solid para-Hydrogen and its Potential Contribution to Interstellar Unidentified Infrared Bands
(2018-10-01)
Sundararajan, Pavithraa
;
Tsuge, Masashi
;
Baba, Masaaki
;
Lee, Yuan-Per
;
交大名義發表
Polycyclic aromatic hydrocarbons (PAH) and their derivatives, including protonated and cationic species, are suspected to be carriers of the unidentified infrared (UIR) emission bands observed from the galactic and extragalactic sources. We extended our investigations of infrared (IR) spectra of protonated planar PAH to a nonplanar PAH, corannulene (C20H10), which is regarded as a fragment of a fullerene, C-60. The protonated corannulene H+C20H10 was produced on bombarding a mixture of corannulene and para-hydrogen (p-H-2) with electrons during deposition at 3.2 K. During maintenance of the electron-bombarded matrix in darkness the intensities of IR lines of protonated corannulene decreased because of neutralization by electrons that were slowly released from the trapped sites. The observed lines were classified into two groups according to their responses to secondary irradiation at 365 nm. Eighteen lines in one group are assigned to the lowest-energy species among five possible isomers, hub-H+C20H10, and 17 in another group to rim-H+C20H10, the species of second lowest energy. Spectral assignments were derived based on a comparison of the observed spectra with those predicted with the B3PW91/6-311++G(2d,2p) method. The observed IR spectrum of hub-H+C20H10 resembles several bands of the Class-A UIR bands.