Charge-transfer State Formation in Supercritical Fluids

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The present study consists of the following four items :1. Raman spectra of 4-N,N-dimethylaminobenzonitrile (DMABN) .2. CARS spectra of molecules forming intramolecular charge-transfer (CT) state.Raman spectra of acetone and CH_3CN in supercritical fluids.4. Charge-transfer state formation in supercritical fluids.The original purpose of this study was to obtain the Raman spectrum of the CT state of DMABN to verify the perpendicularity between the benzene and the dimethylamino planes. However, even with the time-delayd resonance Raman spectroscopy, it turned out that the observation of the Raman spectra of the CT state was quite difficult due to the background fluorescence. Then we attempted to observe the CARS spectrum, again being unsuccessful because of the absence of an appropriate excited state resonant with the Raman excitation.Nevertheless, we gained important information concerning the Raman shift and the CT reaction rate in supercritical fluids as a function of density in the course of the above experiments. The Raman shift contained the rich information on the local environment for the oscillator, which was further analyzed by means of Buckingham's perturbation theory combined with the Percus-Yevick integral equation. Furthermore, the density dependence of the CT formation rate in DMABN was determined in supercritical CF_3H and interpreted in terms of the average clustering number in supercritical solutions.