Rotationally resolved ultrahigh-resolution laser spectroscopy of the S 2A1 1S0A11 transition of azulene

Yosuke Semba, Kazuto Yoshida, Shunji Kasahara, Chi Kung Ni, Yen Chu Hsu, Sheng Hsien Lin, Yasuhiro Ohshima, Masaaki Baba

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Abstract

We have observed rotationally resolved ultrahigh-resolution fluorescence excitation spectra of the 000 (a -type) and 000 +467 cm-1 (b -type) bands of the S2 A1 1 S0 A1 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 S2 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 S0 and S2 states (C2v symmetry). Rotational constants of the S2 state are almost identical to those of the S0 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 S2 A1 1 state of azulene was identified to be IC to the S1B1 2 state. However, this S2 → S1 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 S1 B1 2 state, which is also responsible for the extraordinarily fast S1 → S0 IC in the isolated azulene molecule.

Original languageEnglish
Article number024303
JournalJournal of Chemical Physics
Volume131
Issue number2
DOIs
StatePublished - 2009

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