Intramolecular Vibrational Redistribution in Formic Acid and its Deuterated Forms

TL;DR

This study simulates the vibrational relaxation dynamics of formic acid and its isotopologues, revealing mode couplings and isotopic effects that influence isomerization pathways, with implications for laser control of molecular isomerization.

Contribution

It provides a full-dimensional quantum dynamical analysis of vibrational redistribution in formic acid, highlighting isotopic effects on mode couplings relevant for isomerization control.

Findings

Mode couplings identified between C-O stretch and torsion modes.

Isotopic substitution affects vibrational mode couplings.

Deuteration alters the vibrational relaxation pathways.

Abstract

The intramolecular vibrational relaxation dynamics of formic acid and its deuterated isotopologues is simulated on the full-dimensional potential energy surface of Richter and Carbonniere [F. Richter and P. Carbonniere, J. Chem. Phys., 148, 064303 (2018)] using the Heidelberg MCTDH package. Mode couplings with the torsion coordinate capturing most of the trans-cis isomerisation are identified in the dynamics of artificially excited vibrational mode overtones. The C-O stretch bright vibrational mode is coupled to the out-of-the plane torsion mode in HCOOH, where this coupling could be exploited for laser-induced trans-to-cis isomerisation. Strong isotopic effects are observed: deuteration of the hydroxyl group, i.e., in HCOOD and DCOOD, destroys the C-O stretch to torsion mode coupling whereas in DCOOH, little to no effect is observed.