極短パルスレーザー分光法による超臨界流体中のダイナミクス

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Solvation dynamics and rotational relaxation in supercritical fluids have been examined using the techniques of the subpicosecond laser spectroscopy. The fluorescence up-conversion technique has been employed to detect the fluorescence anisotropy decay of coumarin 153 in supercritical CO2 (310 K) and CHF3 (302, 310 K) over a wide density range. The rotational correlation times in supercritical CHF3 exhibit the remarkable increase at 0.6-0.7 times ρc, which implies that the local solvent density augmentation slows down the rotational dynamics in supercritical fluids. This conclusion is supported by computer simulations based on a 2-site model of fluoroform. The solvation dynamics of the probe 4-dimethylamino-4-cyanostilbene have been measured in supercritical CHF3 at 310 K using the optical Kerr-gated emission technique, which appears to have captured most (∼90%) of the dynamics occurring over the accessible density range between 1.4-2.0ρc. The measured spectral response exhibits a bimodal decay with ∼0.6 ps and ∼9 ps components and only a modest density dependence.
2006-05-20