The ultrafast thermal relaxation of reversed micelles in n-octane/AOT/water (where AOT denotes sodium di-2-ethylhexyl sulfosuccinate) microemulsions was investigated by time-resolved infrared pump-probe spectroscopy. This picosecond cooling process can be described in terms of heat diffusion, demonstrating a new method to determine the nanometer radii of the water droplets. The reverse micelles are stable against transient temperatures far above the equilibrium stability range. The amphiphilic interface layer (AOT) seems to provide an efficient heat contact between the water and the nonpolar solvent.

Efficient intermolecular energy transfer between the C–Br stretching modes ν2 and ν5 of bromoform molecules in the liquid phase has been observed directly in time-resolved experiments applying vibrational pump–probe spectroscopy with picosecond laser pulses. An analysis of results on CHBr3, CDBr3, and an isotopic mixture of both yields a typical time constant of 25±15 ps for this rather efficient, near-resonant intermolecular relaxation channel. Additional new details about the intramolecular pathways of vibrational energy relaxation have been determined for the pure substances.

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Articles you may be interested inVibrational absorption, vibrational circular dichroism, and theoretical studies of methyl lactate self-aggregation and methyl lactate-methanol intermolecular interactions Time-resolved infrared absorption studies of the solvent-dependent vibrational relaxation dynamics of chlorine dioxide J. Chem. Phys. 123, 084503 (2005); 10.1063/1.2000234 Vibrational energy relaxation of aqueous azide ion confined in reverse micelles

The vibrational dynamics of isolated water molecules dissolved in the nonpolar organic liquids 1,2-dichloroethane (C(2)H(4)Cl(2)) and d-chloroform (CDCl(3)) have been studied using an IR pump-probe experiment with approximately 2 ps time resolution. Analyzing transient, time, and spectrally resolved data in both the OH bending and the OH stretching region, the anharmonic constants of the bending overtone (v=2) and the bend-stretch combination modes were obtained. Based on this knowledge, the relaxation pathways of single water molecules were disentangled comprehensively, proving that the vibrational energy of H(2)O molecules is relaxing following the scheme OH stretch-->OH bend overtone-->OH bend-->ground state. A lifetime of 4.8+/-0.4 ps is determined for the OH bending mode of H(2)O in 1,2-dichloroethane. For H(2)O in CDCl(3) a numerical analysis based on rate equations suggests a bending overtone lifetime of tau(020)=13+/-5 ps. The work also shows that full 2-dimensional (pump-probe) spectral resolution with access to all vibrational modes of a molecule is required for the comprehensive analysis of vibrational energy relaxation in liquids.

Intermolecular energy transfer in liquid bromoform and d-bromoform was investigated by help of picosecond IR and Raman spectroscopy. Fora comprehensive interpretation of the corresponding results the study of C-H bending overtone (2V4) relaxation was necessary; the effective vibrational lifetime of this vibrational mode was determined to T1 = 3±1 ps. For the intermolecular transfer a dominating process between the intramolecularly equilibrated C-Br stretching modes V2 and vs of CHBr3 and CDBr3 with a rate constant of 4.10 10 S-l was recognized. Other possible channels, particularly the one between the quasi resonant modes VI (C-D) and 2v4(C-H) were found to be negligible.The question if the intermolecular energy transfer is mainly caused by molecular collisions or if other processes like dipole-dipole interaction play an important role will be an interesting aspect of future work in this field.

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