IR Spectrum of the O-H$...$O Hydrogen Bond of Phthalic Acid Monomethylester in Gas Phase and in CCl$_4$ Solution

TL;DR

This study investigates the IR spectrum of phthalic acid monomethylester's O-H...O hydrogen bond in gas phase and solution, revealing vibrational couplings, resonance effects, and hydrogen motion contributions through advanced modeling and simulations.

Contribution

It combines a five-dimensional gas phase model with QM/MM molecular dynamics to analyze vibrational interactions and hydrogen bond dynamics in different environments.

Findings

Fermi-resonance between OH-stretching and bending overtone identified

Broad absorption band around 3000 cm⁻¹ matches experimental data

Hydrogen motion contributes to weaker absorption features near 2600 cm⁻¹

Abstract

The absorption spectrum of the title compound in the spectral range of the Hydrogen-bonded OH-stretching vibration has been investigated using a five-dimensional gas phase model as well as a QM/MM classical molecular dynamics simulation in solution. The gas phase model predicts a Fermi-resonance between the OH-stretching fundamental and the first OH-bending overtone transition with considerable oscillator strength redistribution. The anharmonic coupling to a low-frequency vibration of the Hydrogen bond leading to a vibrational progression is studied within a diabatic potential energy curve model. The condensed phase simulation of the dipole-dipole correlation function results in a broad band in the 3000 \cm region in good agreement with experimental data. Further, weaker absorption features around 2600 \cm have been identified as being due to motion of the Hydrogen within the Hydrogen bond.