Dynamics of the Cl + CH3CN reaction on an automatically-developed full-dimensional ab initio potential energy surface.

J Chem Phys

MTA-SZTE Lendület Computational Reaction Dynamics Research Group, Interdisciplinary Excellence Centre and Department of Physical Chemistry and Materials Science, Institute of Chemistry, University of Szeged, Rerrich Béla tér 1, Szeged H-6720, Hungary.

Published: August 2024

AI Article Synopsis

  • A new potential energy surface (PES) has been created for the Cl + CH3CN chemical reaction, building on previous research that accurately identified stationary points of the reaction.
  • The PES is achieved using advanced fitting methods, and simulations at various collision energies reveal several low-probability reaction pathways, with H-abstraction being the most significant.
  • As collision energy increases, the reaction dynamics shift from indirect/rebound mechanisms to direct stripping, with the products showing various energy distributions—HCl mainly in the ground vibrational state and CH2CN with notable vibrational excitation.

Article Abstract

A full-dimensional analytical potential energy surface (PES) is developed for the Cl + CH3CN reaction following our previous work on the benchmark ab initio characterization of the stationary points. The spin-orbit-corrected PES is constructed using the Robosurfer program and a fifth-order permutationally invariant polynomial method for fitting the high-accuracy energy points determined by a ManyHF-based coupled-cluster/triple-zeta-quality composite method. Quasi-classical trajectory simulations are performed at six collision energies between 10 and 60 kcal mol-1. Multiple low-probability product channels are found, including isomerization to isonitrile (CH3NC), but out of the eight possible channels, only the H-abstraction has significant reaction probability; thus, detailed dynamics studies are carried out only for this reaction. The cross sections and opacity functions show that the probability of the H-abstraction reaction increases with increasing collision energy (Ecoll). Scattering angle, initial attack angle, and product relative translational energy distributions indicate that the mechanism changes with the collision energy from indirect/rebound to direct stripping. The distribution of initial attack angles shows a clear preference for methyl group attack but with different angles at different Ecoll values. Post-reaction energy distributions show that the energy transfer is biased toward the products' relative translational energy instead of their internal energy. Rotational and vibrational energy have about the same amount of contribution to the internal energy in the case of both products (HCl and CH2CN), i.e., both of them are formed with high rotational excitations. HCl is produced mostly in the ground vibrational state, while a notable fraction of CH2CN is formed with vibrational excitation.

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Source
http://dx.doi.org/10.1063/5.0220917DOI Listing

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