# Energy relaxation and thermal diffusion in IR pump-probe spectroscopy of hydrogen-bonded liquids

## TL;DR

This paper uses molecular dynamics simulations to distinguish between vibrational relaxation and thermal diffusion in IR pump-probe spectroscopy of hydrogen-bonded liquids, revealing how transient hydrogen bond structures influence heat transfer.

## Contribution

It demonstrates that vibrational relaxation and thermal diffusion are decoupled processes occurring on different scales, providing insights into the molecular dynamics of hydrogen-bonded liquids.

## Key findings

- Vibrational relaxation occurs faster than heat diffusion.
- Transient hydrogen bond structures affect thermal diffusivity.
- Thermal relaxation involves nanometer-scale structural influences.

## Abstract

Infrared pump-probe spectroscopy provides detailed information on the dynamics of hydrogen-bonded liquids. Due to dissipation of the absorbed pump pulse energy, also thermal equilibration dynamics contributes to the observed signal. Disentangling this contribution from the molecular response remains an open challenge. Performing non-equilibrium molecular dynamics simulat ions of liquid deuterated methanol, we show that faster molecular vibrational relaxation and slower heat diffusion are decoupled and occur on different length scale. Transient structures of the hydrogen bonding network influence thermal relaxation by affecting thermal diffusivity over the length-scale of several nanometers.