Intramolecular vibrational redistribution in formic acid and its deuterated forms

Area of Science:

• Chemical Physics
• Molecular Dynamics
• Spectroscopy

Background:

• Intramolecular vibrational relaxation (IVR) governs energy flow in molecules.
• Understanding IVR is crucial for controlling chemical reactions and photophysical processes.
• Formic acid serves as a model system for studying fundamental IVR dynamics.

Purpose of the Study:

• To simulate the IVR dynamics of formic acid and its deuterated isotopologues.
• To investigate the coupling between vibrational modes, particularly the C-O stretch and torsion modes.
• To explore the potential for laser-induced trans-cis isomerization via vibrational mode excitation.

Main Methods:

• Full-dimensional potential energy surface calculations.
• Heidelberg Multiconfiguration Time-Dependent Hartree (MCTDH) package for dynamics simulations.
• Analysis of vibrational mode couplings and energy transfer pathways.

Main Results:

• The C-O stretch vibrational mode is coupled to the out-of-the-plane torsion mode in formic acid (HCOOH).
• Strong isotopic effects were observed upon deuteration.
• Deuteration of the hydroxyl group (HCOOD, DCOOD) disrupts this coupling, while deuteration in DCOOH shows minimal effect.

Conclusions:

• The observed isotopic effects significantly influence the vibrational energy flow and isomerization potential.
• Laser-induced isomerization via C-O stretch excitation is feasible in HCOOH but strongly affected by deuteration.
• This study provides insights into mode-specific vibrational dynamics and isotopic effects in small molecules.