Quantum mechanical tunneling in the automerization of cyclobutadiene

Schoonmaker, R.; Lancaster, T.; Clark, S.J.

Abstract

Cyclobutadiene has a four-membered carbon ring with two double bonds, but this highly strained molecular configuration is almost square and, via a coordinated motion, the nuclei quantum mechanically tunnels through the high-energy square state to a configuration equivalent to the initial configuration under a 90° rotation. This results in a square ground state, comprising a superposition of two molecular configurations, that is driven by quantum tunneling. Using a quantum mechanical model, and an effective nuclear potential from density functional theory, we calculate the vibrational energy spectrum and the accompanying wavefunctions. We use the wavefunctions to identify the motions of the molecule and detail how different motions can enhance or suppress the tunneling rate. This is relevant for kinematics of tunneling-driven reactions, and we discuss these implications. We are also able to provide a qualitative account of how the molecule will respond to an external perturbation and how this may enhance or suppress infra-red-active vibrational transitions.

Citation

Schoonmaker, R., Lancaster, T., & Clark, S. (2018). Quantum mechanical tunneling in the automerization of cyclobutadiene. The Journal of Chemical Physics, 148(10), Article 104109. https://doi.org/10.1063/1.5019254

• Journal Article Type: Article
• Acceptance Date: Feb 21, 2018
• Online Publication Date: Mar 12, 2018
• Publication Date: Mar 12, 2018
• Deposit Date: Mar 13, 2018
• Publicly Available Date: Mar 13, 2018
• Journal: Journal of Chemical Physics
• Print ISSN: 0021-9606
• Electronic ISSN: 1089-7690
• Publisher: American Institute of Physics
• Peer Reviewed: Peer Reviewed
• Volume: 148
• Issue: 10
• Article Number: 104109
• DOI: https://doi.org/10.1063/1.5019254
• Public URL: https://durham-repository.worktribe.com/output/1333079