Browsing by Author "Semba, Yosuke"

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Rotationally resolved ultrahigh-resolution laser spectroscopy of the S(2) (1)A(1)<- S(0) (1)A(1) transition of azulene
(2009-07-14)
Semba, Yosuke
;
Yoshida, Kazuto
;
Kasahara, Shunji
;
Ni, Chi-Kung
;
Hsu, Yen-Chu
We have observed rotationally resolved ultrahigh-resolution fluorescence excitation spectra of the 0(0)(0) (a-type) and 0(0)(0)+467 cm(-1) (b-type) bands of the S(2) (1)A(1)<- S(0) (1)A(1) transition of jet-cooled azulene. The observed linewidth is 0.0017 cm(-1), which corresponds to the lifetime of 3.1 ns in the S(2) state. Zeeman splitting of rotational lines is very small so that intersystem crossing to the triplet state is considered to be very slow. Inertial defect is very small and the molecule is considered to be planar in the S(0) and S(2) states (C(2 upsilon) symmetry). Rotational constants of the S(2) state are almost identical to those of the S(0) state, indicating that geometrical structure is similar in both electronic states. In this case, internal conversion (IC) by vibronic coupling is thought to be inactive. Therefore, the main radiationless transition process in the S(2) (1)A(1) state of azulene was identified to be IC to the S(1) (1)B(2) state. However, this S(2)-> S(1) IC is still slower than that of conventional polycyclic aromatic hydrocarbons. We consider it to be due to the shallower potential energy curve in the S(1) (1)B(2) state, which is also responsible for the extraordinarily fast S(1)-> S(0) IC in the isolated azulene molecule. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3168394]
Rotationally resolved ultrahigh-resolution laser spectroscopy of the S-2 (1)A(1)<- S-0 (1)A(1) transition of azulene
(2009-07-14)
Semba, Yosuke
;
Yoshida, Kazuto
;
Kasahara, Shunji
;
Ni, Chi-Kung
;
Hsu, Yen-Chu
We have observed rotationally resolved ultrahigh-resolution fluorescence excitation spectra of the 0(0)(0) (a-type) and 0(0)(0)+467 cm(-1) (b-type) bands of the S-2 (1)A(1)<- S-0 (1)A(1) transition of jet-cooled azulene. The observed linewidth is 0.0017 cm(-1), which corresponds to the lifetime of 3.1 ns in the S-2 state. Zeeman splitting of rotational lines is very small so that intersystem crossing to the triplet state is considered to be very slow. Inertial defect is very small and the molecule is considered to be planar in the S-0 and S-2 states (C-2 upsilon symmetry). Rotational constants of the S-2 state are almost identical to those of the S-0 state, indicating that geometrical structure is similar in both electronic states. In this case, internal conversion (IC) by vibronic coupling is thought to be inactive. Therefore, the main radiationless transition process in the S-2 (1)A(1) state of azulene was identified to be IC to the S-1 B-1(2) state. However, this S-2 -> S-1 IC is still slower than that of conventional polycyclic aromatic hydrocarbons. We consider it to be due to the shallower potential energy curve in the S-1 B-1(2) state, which is also responsible for the extraordinarily fast S-1 -> S-0 IC in the isolated azulene molecule. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3168394]
Vibrational and rotational structure and excited-state dynamics of pyrene
(1970-01-01)
Baba, Masaaki
;
Saitoh, Motohisa
;
Kowaka, Yasuyuki
;
Taguma, Kunio
;
Yoshida, Kazuto
"Vibrational level structure in the S-0 (1)A(g) and S-1 B-1(3u) states of pyrene was investigated through analysis of fluorescence excitation spectra and dispersed fluorescence spectra for single vibronic level excitation in a supersonic jet and through referring to the results of ab initio theoretical calculation. The vibrational energies are very similar in the both states. We found broad spectral feature in the dispersed fluorescence spectrum for single vibronic level excitation with an excess energy of 730 cm(-1). This indicates that intramolecular vibrational redistribution efficiently occurs at small amounts of excess energy in the S-1 B-1(3u) state of pyrene. We have also observed a rotationally resolved ultrahigh-resolution spectrum of the 0(0)(0) band. Rotational constants have been determined and it has been shown that the pyrene molecule is planar in both the S-0 and S-1 states, and that its geometrical structure does not change significantly upon electronic excitation. Broadening of rotational lines with the magnetic field by the Zeeman splitting of M-J levels was very small, indicating that intersystem crossing to the triplet state is minimal. The long fluorescence lifetime indicates that internal conversion to the S-0 state is also slow. We conclude that the similarity of pyrene's molecular structure and potential energy curve in its S-0 and S-1 states is the main cause of the slow radiationless transitions."