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Issue 28, 2019

Electronic transitions of molecules: vibrating Lewis structures

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Abstract

Since the conception of the electron pair bond, Lewis structures have been used to illustrate the electronic structure of a molecule in its ground state. But, for excited states, most descriptions rely on the concept of molecular orbitals. In this work we demonstrate a simple and intuitive description of electronic resonances in terms of localized electron vibrations. By partitioning the 3N-dimensional space of a many-electron wavefunction into hyper-regions related by permutation symmetry, chemical structures naturally result which correspond closely to Lewis structures, with identifiable single and double bonds, and lone pairs. Here we demonstrate how this picture of electronic structure develops upon the admixture of electronic wavefunctions, in the spirit of coherent electronic transitions. We show that π–π* transitions correspond to double-bonding electrons oscillating along the bond axis, and n–π* transitions reveal lone-pairs vibrating out of plane. In butadiene and hexatriene, the double-bond oscillations combine with in- and out-of-phase combinations, revealing the correspondence between electronic transitions and molecular normal mode vibrations. This analysis allows electronic excitations to be described by building upon ground state electronic structures, without the need for molecular orbitals.

Graphical abstract: Electronic transitions of molecules: vibrating Lewis structures

Article information


Submitted
24 May 2019
Accepted
02 Jun 2019
First published
11 Jun 2019

This article is Open Access
All publication charges for this article have been paid for by the Royal Society of Chemistry

Chem. Sci., 2019,10, 6809-6814
Article type
Edge Article

Electronic transitions of molecules: vibrating Lewis structures

Y. Liu, P. Kilby, T. J. Frankcombe and Timothy W. Schmidt, Chem. Sci., 2019, 10, 6809 DOI: 10.1039/C9SC02534K

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