Temperature-independent non-linear terahertz transmission by liquid water

TL;DR

This study demonstrates that the non-linear terahertz transmission of liquid water at around 1 THz is temperature-independent between 21°C and 4°C, supporting models based on resonant reorientation of water molecules.

Contribution

It provides evidence that the non-linear terahertz response of water is weakly dependent on temperature, favoring specific microscopic models of water dynamics.

Findings

Non-linear terahertz transmission is equal at 21°C and 4°C.

Supports resonant reorientation as the key mechanism.

Temperature independence suggests weak temperature dependence of water's non-linear response.

Abstract

Liquid water is one of the most studied substances, yet many of its properties are difficult to rationalize. The uniqueness of water is rooted in the dynamic network of hydrogen-bonded molecules with relaxation time constants of about one picosecond. Terahertz fields oscillate on a picosecond timescale and are inherently suited to study water. Recent advances in non-linear terahertz spectroscopy have revealed large signals from water, which have been interpreted with different, sometimes competing, theoretical models. Here we show that the non-linear transmission of liquid water at ~1 THz is equal at 21 {\deg}C and 4 {\deg}C, thus suggesting that the most appropriate microscopic models should depend weakly on temperature. Among the different mechanisms proposed to date, the resonant reorientation of hydrogen-bonded water molecules might be the most appropriate to describe all of the currently available experimental results.