The CN(X 2Σ+) + C2H6 reaction: Dynamics study based on an analytical full-dimensional potential energy surface

Area of Science:

• Chemical Dynamics
• Theoretical Chemistry
• Reaction Mechanisms

Background:

• The reaction of cyano radicals with ethane is crucial for understanding chemical processes across various temperature regimes.
• Investigating the vibrational distribution of the hydrogen cyanide (HCN) product is key to elucidating reaction dynamics.

Purpose of the Study:

• To develop a high-accuracy, full-dimensional analytical potential energy surface (PES-2023) for the cyano radical-ethane reaction.
• To perform quasi-classical trajectory (QCT) calculations to study the reaction dynamics at room temperature.
• To analyze the vibrational and rotational energy distributions of the HCN product and compare with experimental findings.

Main Methods:

• Development of an analytical full-dimensional potential energy surface (PES-2023) using valence bond and molecular mechanics terms.
• Fitting PES-2023 to high-level ab initio calculations (explicitly correlated CCSD(T)-F12/aug-cc-pVTZ).
• Execution of quasi-classical trajectory (QCT) calculations on PES-2023 to simulate the reaction dynamics.

Main Results:

• PES-2023 accurately describes the reaction topology, including high exothermicity, a low barrier, and intermediate complexes.
• QCT calculations show that available energy is primarily channeled into HCN vibrational modes, with inverted CH stretching excitation.
• The model reproduces experimental observations for vibrational population inversion and reveals cold rotational distributions and backward scattering.

Conclusions:

• PES-2023 provides a reliable description of the cyano radical-ethane reaction dynamics.
• The study clarifies the energy disposal mechanisms in the reaction, particularly the vibrational excitation of HCN.
• The findings contribute to a deeper understanding of chemical kinetics from low to high-temperature environments.