Dephasing of Local Vibrations in a Planar Lattice of Adsorbed Molecules

TL;DR

This paper models how low-frequency vibrations in a molecular lattice cause dephasing of high-frequency local vibrations, revealing that lateral interactions can narrow spectral lines, aligning with experimental observations.

Contribution

It introduces a Green's function approach to describe dephasing in a lattice of adsorbed molecules, accounting for anharmonic coupling and resonance effects.

Findings

Lateral interactions can significantly narrow high-frequency spectral lines.

Spectral line positions and widths depend on dispersion laws and mode lifetimes.

The model's predictions are consistent with experimental data.

Abstract

We investigate anharmonically coupled high- and low-frequency excitations in a planar lattice of adsorbed molecules interacting with phonons of a crystal. Dephasing of high-frequency local vibrations by low-frequency resonance modes is described in terms of temperature Green's function. The equations obtained are solved, first, with a small ratio of the anharmonic coupling coefficient for high- and low-frequency modes to the resonance width, and second, in the low-temperature limit. High-frequency spectral line positions and widths depend on dispersion laws and resonance mode lifetimes. It is shown that lateral interactions of low-frequency modes of adsorbed molecules can lead to a significant narrowing of high-frequency spectral lines, which is consistent with experimental data.