Formic acid dimerization: evidence for species diversity from first principles simulations

Area of Science:

• Computational Chemistry
• Physical Chemistry
• Spectroscopy

Background:

• Understanding molecular aggregation is crucial for chemical processes.
• Formic acid dimerization provides a model system for studying hydrogen bonding and reaction dynamics.

Purpose of the Study:

• To simulate formic acid dimerization using ab initio molecular dynamics.
• To investigate aggregation product distributions and reaction pathways at various temperatures.
• To predict theoretical vibrational spectra for experimental identification of dimer species.

Main Methods:

• Ab initio molecular dynamics simulations.
• Targeted molecular dynamics and thermodynamic integration for free-energy barrier calculations.
• Analysis of aggregation product distributions and reaction pathways.

Main Results:

• Cyclic dimer (structure A) predominates at high temperatures.
• Acyclic dimer (structure B) is the main species at low temperatures.
• Two additional, less stable dimer species (C and D) are predicted at low temperatures.
• Free-energy barrier for C to A interconversion is 7.0 kJ/mol, indicating stabilization at ultracold conditions.

Conclusions:

• The study elucidates temperature-dependent formic acid dimerization.
• Predicted dimer species and vibrational spectra can guide experimental research.
• Findings are relevant for low-temperature spectroscopy in matrix isolation and helium droplet experiments.