Abstract
Abstract Hydrogen-bonded mixtures with varying concentration are a complicated networked system that demands a detection technique with both time and frequency resolutions. Hydrogen-bonded pyridine–water mixtures are studied by a time-frequency resolved coherent Raman spectroscopic technique. Femtosecond broadband dual-pulse excitation and delayed picosecond probing provide sub-picosecond time resolution in the mixtures temporal evolution. For different pyridine concentrations in water, asymmetric blue versus red shifts (relative to pure pyridine spectral peaks) were observed by simultaneously recording both the coherent anti-Stokes and Stokes Raman spectra. Macroscopic coherence dephasing times for the perturbed pyridine ring modes were observed in ranges of 0.9–2.6 ps for both 18 and 10 cm − 1 10\hspace{0.33em}{{\rm{cm}}}^{-1} broad probe pulses. For high pyridine concentrations in water, an additional spectral broadening (or escalated dephasing) for a triangular ring vibrational mode was observed. This can be understood as a result of ultrafast collective emissions from coherently excited ensemble of pairs of pyridine molecules bound to water molecules.
Highlights
Hydrogen-bonded mixtures with varying concentration are a complicated networked system that demands a detection technique with both time and frequency resolutions
We adopt the coherent anti-Stokes Raman scattering (CARS)/CSRS spectroscopy developed in refs. [23,24], which involves three ultrashort pulses: the fs pump and fs Stokes pulses selectively excite the pyridine ring breathing mode at ν1 (992 cm−1) and triangular mode at ν12 ( 1,031 cm−1) with a separation of 39 cm−1 into their macroscopic coherence with a negligible contribution from the background water solvent molecules and the ps probe pulse is scattered off to produce signal to be recorded in the forward direction
For different pyridine concentrations in water both coherent anti-Stokes and Stokes Raman spectra were recorded as functions of probe delay
Summary
Abstract: Hydrogen-bonded mixtures with varying concentration are a complicated networked system that demands a detection technique with both time and frequency resolutions. Hydrogen-bonded pyridine–water mixtures are studied by a time-frequency resolved coherent Raman spectroscopic technique. Macroscopic coherence dephasing times for the perturbed pyridine ring modes were observed in ranges of 0.9–2.6 ps for both 18 and 10 cm−1 broad probe pulses. For high pyridine concentrations in water, an additional spectral broadening (or escalated dephasing) for a triangular ring vibrational mode was observed. This can be understood as a result of ultrafast collective emissions from coherently excited ensemble of pairs of pyridine molecules bound to water molecules
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