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Enhancement of the Stimulated Raman Scattering of Benzene−Toluene Mixtures under Strong Excitation Condition in the Liquid Phase

Hiroharu Yui,^† Takahito Nakajima,^‡ Kimihiko Hirao,^‡ and Tsuguo Sawada*^†^‡^§

Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology Corporation (JST), Saitama, Kawaguchi City 332-0012, Japan, and Department of Applied Chemistry, Graduate School of Engineering, and Department of Advanced Materials Science, Graduate School of Frontier Science, The University of Tokyo, 7-3-1 Bunkyo, Hongo, Tokyo 113-0033, Japan

J. Phys. Chem. A, 2003, 107 (7), pp 968–973

DOI: 10.1021/jp021993l

Publication Date (Web): January 28, 2003

†

Core Research for Evolutional Science and Technology.

‡

Department of Applied Chemistry.

To whom all correspondence should be addressed.

Department of Advanced Materials Science.

Abstract

Anomalous enhancement of stimulated Raman scattering (SRS) of the aromatic CH stretching band was observed when the laser-induced plasma was generated in benzene−toluene mixed solvents. Time-resolved spectra of the SRS revealed that the strong excitation condition which led to generation of ionized molecules played an important role in anomalous enhancement. The observed intensity dependence on the mixture ratio meant that the complex formation between benzene and ionized toluene molecules contributed to its enhancement. Results of the theoretical calculation indicated that the Raman cross section of benzene and toluene molecules was remarkably enhanced due to the charge distribution between benzene and toluene cations compared to the Raman cross section in each neutral monomer state. The mechanism of the anomalous enhancement was considered in terms of the formation of cationic benzene−toluene complexes under the strong excitation condition and subsequent change of the Raman cross section due to the charge-resonant interaction in the cationic complexes.

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