Ultrafast dephasing in hydrogen-bonded pyridine-water mixtures

TL;DR

This study uses advanced time-frequency coherent Raman spectroscopy to investigate ultrafast dephasing dynamics in hydrogen-bonded pyridine-water mixtures, revealing concentration-dependent spectral shifts and coherence times.

Contribution

It introduces a novel application of femtosecond broadband dual-pulse excitation combined with picosecond probing to analyze ultrafast molecular dephasing in hydrogen-bonded systems.

Findings

Observed asymmetric spectral shifts with concentration.

Measured sub-picosecond coherence dephasing times.

Detected additional spectral broadening at high pyridine concentrations.

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 picoseconds 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.