Related Experiment Video
Updated: Jun 8, 2026

Excitonic Hamiltonians for Calculating Optical Absorption Spectra and Optoelectronic Properties of Molecular Aggregates and Solids
Published on: May 27, 2020
Communication: Effective spectroscopic Hamiltonian for multiple minima with above barrier motion: Isomerization in
George L Barnes1, Michael E Kellman
1Department of Chemistry and Institute of Theoretical Science, University of Oregon, Eugene, Oregon 97403, USA.
Abstract:
We present a two-dimensional potential surface for the isomerization in the hydroperoxyl radical HO(2) and calculate the vibrational spectrum. We then show that a simple effective spectroscopic fitting Hamiltonian is capable of reproducing large scale vibrational spectral structure above the isomerization barrier. Polyad breaking with multiple resonances is necessary to adequately describe the spectral features of the system. Insight into the dynamical nature of isomerization related to the effective Hamiltonian is gained through classical trajectories on the model potential. Contrary to physical intuition, the bend mode is not a "reaction mode," but rather isomerization requires excitation in both stretch and bend. The dynamics reveals a Farey tree formed from the 2:1 and 3:1 resonances, corresponding to the resonance coupling terms in the effective Hamiltonian, with the prominent 5:2 (2:1+3:1) feature dividing the tree into parts that we call the 3:1 and 2:1 portions.
Related Concept Videos
¹H NMR of Conformationally Flexible Molecules: Temporal Resolution
UV–Vis Spectroscopy: Molecular Electronic Transitions
π Molecular Orbitals of 1,3-Butadiene
The simplest conjugated diene is 1,3-butadiene: a four-carbon system where each carbon is sp2-hybridized and has an unhybridized p orbital that contains an unpaired electron. According to molecular orbital theory, atomic orbitals combine to form molecular orbitals such that the number...
Molecular Orbital Theory II
¹H NMR: Interpreting Distorted and Overlapping Signals
As Δν decreases and the signals move closer, the doublets appear increasingly distorted. The intensities of the inner lines increase at the cost of those of the outer lines as the signals are slanted or...
Regioselectivity and Stereochemistry of Hydroboration
Hydroboration proceeds in a concerted fashion with the attack of borane on the π bond, giving a cyclic four-centered transition state. The –BH2 group is bonded to the less substituted carbon and –H to the more substituted carbon. The concerted nature requires the simultaneous addition of –H and –BH2 across the same face of the alkene giving syn stereochemistry.

