Spectral hole burning is observed for the OH stretching mode of HDO dissolved in D2O at 298 K after intense infrared excitation. Three spectral components are inferred from the transient band shapes and related to an icelike molecular environment and other hydrogen-bonding configurations. A population lifetime of T\ =8 ± 2 ps and an anharmonic frequency shift of 270 ± 20 cm ~] are measured.PACS numbers: 61.25. Em, 33.20.Ea, 42.65.Ft, 78.47.+p It is commonly believed that the properties of the OH stretching vibration are strongly related to the structure of the hydrogen bridge bond. Vibrational spectroscopy was, therefore, widely used in the past to investigate hydrogen-bonded systems. 1 For some liquids, e.g., alcohols, ir-absorption studies allow the determination of a few different hydrogen-bonded species and of the corresponding association parameters. 2 Matrix isolation techniques show that a larger number of transition frequencies can be discerned. 3 The relation of these observations to liquids is not well understood. For water, the situation is particularly complicated, since each molecule can form up to four hydrogen bonds. Several attempts have been reported to deduce structural information on this system from infrared, Raman, or attenuated-totalreflectance spectroscopy. 4 These results gave some evidence for a discrete substructure of the OH absorption that was attributed to different hydrogen-bonded environments. A final answer to such questions is still lacking; obviously more powerful spectroscopic techniques are required, e.g., time-resolved infrared spectroscopy 5 as demonstrated very recently for a H-bonded polymer. 6 In this Letter spectral hole burning on the picosecond time scale is reported for the first time for the vibrational spectrum of HDO dissolved in D2O. Direct evidence is obtained for a discrete substructure of the OH stretching band at 3400 cm" 1 . Three spectral components are deduced from the transient band shapes supporting a multicomponent model of water. 7 Details of the experimental system were described recently. 5 In short, a first intense ir pulse (energy -50 juJ, duration 11 ±2 ps, bandwidth 18 ±2 cm" 1 around 3400 cm -1 ) is tuned to the desired excitation frequency and resonantly pumps the OH stretching mode. A second, independently tunable, weak pulse probes the sample transmission T(VJD) as a function of delay time to or probe frequency v; to = 0 marks the maximum of the pump pulse. Most of the measurements are performed with parallel polarization of the excitation and interrogation pulses. The common small-signal transmission To(v) is measured blocking the pump beam.The samples (length 100 //m) were 0.5-1 mol/1 HDO in D2O prepared by mixing corresponding amounts of demineralized, bidistilled H2O in highly purified D 2 0 (99.996% isotopic purity). After proton exchange, the residual H2O content of the samples was less than 0.01 mol/1. Figure 1 (a) shows the absorption band of a HDO sample (1 mol/1, experimental points) obtained by a commercial infrared spectrometer a...

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Internal, hydrogen bonded OH groups of ethanol oligomers (solvent CCl4) are vibrationally excited by intense picosecond pulses at 3320 cm−1. The transient band shape observed in the OH stretching region (3000 to 3700 cm−1) is monitored by an independently tunable picosecond infrared pulse. The bands in this region are direct probes of hydrogen bridges. The time dependent growth and decay of these bands provides strong evidence for rapid bond breaking with a vibrational predissociation time of ≊5 ps, and for partial reassociation with a time constant of ≊20 ps.

The state of information about vibrational population relaxation in the liquid state is still rather scarce. By using incoherent anti-Stokes scattering after strong infrared excitation, it is now possible to obtain rather complete information about these relaxation processes. In this paper we will report a study on the chloroform molecule. As all vibrations of this molecule are Raman active, they can be investigated by this experimental approach. Population lifetimes between 23 and several hundred ps are found. This is, to our knowledge, the first measurement displaying simultaneously the time evolution of all fundamentals of a molecule after direct population of a vibrational state.

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.