Browsing by Author "Otsubo, Tetsuo"

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Chirped modulation of molecular vibration in quinoidal thiophene after sub-5 fs excitation
(2006-10-19)
Wang, Zhuan
;
Otsubo, Tetsuo
;
Kobayashi, Takayoshi
;
電子物理學系
;
Department of Electrophysics
Fourier transformation of the real-time trace of sub-5 fs pump-induced molecular vibration in quinoidal thiophene in solution revealed coupled modes to the electronic excitation at 206, 447, and 1466 cm(-1). Spectrogram analysis of 1466 cm(-1) (C=C stretching) mode showed that the amplitude and frequency of the mode are modulated with another low-frequency mode at about 220 cm(-1), which is down chirped being induced by the coupling with modes of even lower frequency, resulting in the irreversible relaxation due to high mode density in the low-frequency range. This Letter thus reports on observation of the modulation of vibrational frequency with a chirped frequency. (c) 2006 Elsevier B.V. All rights reserved.
Classification of dynamic vibronic couplings in vibrational real-time spectra of a thiophene derivative by few-cycle pulses
(2007-12-20)
Kobayashi, Takayoshi
;
Wang, Zhuan
;
Otsubo, Tetsuo
;
電子物理學系
;
Department of Electrophysics
Pump-probe spectroscopy was performed with a few cycle pulses of 6.7 fs duration. The electronic transition intensity modulation was induced by molecular vibration in a quinoid thiophene molecule in solution. The real-time vibrational features were analyzed in terms of dependence of vibrational amplitude and phase on probe photon energy. The electronic transition probability is modulated by molecular vibration via vibronic coupling. Changes in the spectral shape and intensity of the time-resolved spectrum were studied by tracking characteristic spectral features including the peak frequency and intensity, spectral bandwidth, and band-integrated intensity. From the analysis the modulation mechanisms were classified into two groups: (1) Condon type and (2) non-Condon type. The features of the wave packet motions were also classified into zeroth-order derivatives due to quasi-pure non-Condon type and first- and second-order derivative types due to the displacement of the potential minimum and the potential curvature change associated with the relevant vibronic transition, respectively.
Confined breather-type excitation in a quinoidal thiophene after sub-5 fs pulse excitation
(2006-07-28)
Kobayashi, Takayoshi
;
Wang, Haibo
;
Wang, Zhuan
;
Otsubo, Tetsuo
;
電子物理學系
A quinoidal thiophene molecule which is a prototype of the repeated unit of s-trans-cis-polyacetylene was studied by sub-5 fs spectroscopy. A breatherlike mode modulation of both the amplitude and frequency of the C = C stretching was observed for the first time. It generates two sidebands of 2238 and 700 cm(-1) with a separation of 769 cm(-1) corresponding to the modulation frequency. The latter mode is very close to the C-S-C ring deformation, which indicate that this mode mediates coupling between the breather mode and the C-beta-C-beta stretching mode. It was also found that the breather-type excitation has a longer lifetime (2-3 ps) than in all-trans-polyacetylene (50 fs) due to its confinement. (c) 2006 American Institute of Physics.
Sub-5-fs spectroscopy of a thiophene derivative with a quinoid structure
(2006-07-26)
Kobayashi, Takayoshi
;
Wang, Haibo
;
Wang, Zhuan
;
Otsubo, Tetsuo
;
電子物理學系
Sub-5-fs spectroscopy of a thiophene derivative with an electron donative and an acceptive moieties and quinoid structure provided the experimental evidence of dynamic mode coupling. It was shown that two out-of-plane bending modes mediate the dynamic mode coupling between 1469 and 1379 cm(-1) and between 1603 and 1469 cm(-1). These couplings are considered to be associated with geometrical relaxation relevant to the neutral bipolaron formation in all-s-trans polyacetylene. (c) 2006 Elsevier B.V. All rights reserved.