Classical dynamics study of HONO using constrained trajectories

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Abstract
Constrained classical trajectory calculations were carried out to investigate intramolecular vibrational energy redistribution (IVR), cis–trans isomerization, and rotation–vibration interactions in HONO. Relaxation of the OH bond stretching mode, initially excited to the second overtone state, was monitored by using a local-mode approximation. In order to determine the roles of the various modes in the IVR and cis–trans isomerization, the dihedral, HON bending, or ONO bending angle was dynamically constrained by incorporating Lagrangian multipliers into Hamilton’s equations of motion. The results show that the in-plane HON bending and out-of-plane torsional motions play important roles in the IVR. A strong interaction between the torsional and HON bending modes is a major factor in causing cis-HONO to isomerize at significantly greater rates than trans-HONO. Molecular rotation significantly enhances IVR, however, it has little effect when the torsional coordinate is frozen at its equilibrium value.