Comment on: "Tunneling of coupled methyl quantum rotors in 4-methylpyridine: Single rotor potential versus coupling interaction". J. Chem. Phys. \textbf{147}, 194303 (2017)

TL;DR

This paper critiques and clarifies previous findings on coupled methyl rotors, demonstrating that an avoided crossing is actually a true crossing of different symmetries, using group theory for more accurate analysis.

Contribution

It provides a clearer analysis of coupled methyl rotor energy levels by applying group theory and independent eigenvalue calculations, correcting prior interpretations.

Findings

Identified a true crossing between states of different symmetry.

Demonstrated the effectiveness of group theory in rotor analysis.

Provided more accurate eigenvalue calculations for coupled rotors.

Abstract

We analyze the results obtained recently by Khazael and Sebastiani (J. Chem. Phys. \textbf{147}, 194303 (2017)) for two coupled methyl rotors. We show that one of the avoided crossings obtained by those authors is in fact a true crossing between states of different symmetry. Present analysis is supposed to be clearer because it is based on an independent calculation of eigenvalues for each irreducible representation. The application of group theory also enables a more accurate calculation by means of smaller matrix representations of the Hamiltonian operator.