Browsing by Author "Sakurai, Hidehiro"

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Electronic and vibrational structure in the S-0 and S-1 states of corannulene
(2019-12-21)
Kanaoka, Ayumi
;
Tohyama, Hiromi
;
Kunishige, Sachi
;
Katori, Toshiharu
;
Nishiyama, Akiko
Corannulene is a nonplanar aromatic hydrocarbon also known as a buckybowl. Its electronic and vibrational structure has been investigated by analyzing its fluorescence excitation spectrum and dispersed fluorescence spectrum in a supersonic jet. Its spectral features are in keeping with the expectation, confirmed by some previous results, that it has fivefold or C-5 nu, symmetry. The observed prominent vibronic bands in the S-1 <- S-0 transition have been assigned to e(1) and e(2) bands on the basis of theoretical calculations so that the S-1 state was assigned to E-1(2). The symmetry adapted cluster configuration interaction calculation supports this assignment of the S, electronic state, although the time-dependent density functional theory calculation suggests that the S-1 state is (1)A(2). It has also been shown that the normal coordinates for strong vibronic bands mainly include out-of-plane vibrational motion. The rotational envelopes are well explained by taking account of the Coriolis interaction between the degenerate vibrational and rotational levels. The mechanism of bowl-to-bowl inversion is also discussed with the results of theoretical calculations regarding the barrier to inversion and metastable conformation. Published under license by AIP Publishing.
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.