Jump to main content
Jump to site search

Issue 47, 2020

Role of hemibonding in the structure and ultraviolet spectroscopy of the aqueous hydroxyl radical

Author affiliations

Abstract

The presence of a hemibond in the local solvation structure of the aqueous hydroxyl radical has long been debated, as its appearance in ab initio simulations based on density functional theory is sensitive to self-interaction error (favoring a two-center, three-electron hemibond) but also to finite-size effects. Simulations reported here use a mixed quantum mechanics/molecular mechanics (QM/MM) framework in a very large periodic simulation cell, in order to avoid finite-size artifacts and to facilitate testing of various density functionals, in order to probe the effects of delocalization error. The preponderance of hemibonded structures predicted by generalized gradient approximations persists in simulations using the hybrid functionals B3LYP and PBE0, but is reduced to a minor population if the fraction of exact exchange is increased to 50%. The hemibonded population is also small in simulations employing the long-range corrected functional LRC-ωPBE. Electronic spectra are computed using time-dependent density functional theory, and from these calculations emerges a consensus picture in which hemibonded configurations play an outsized role in the absorption spectrum, even when present as a minority species. An intense 1b2(H2O) → 2pπ(˙OH) charge-transfer transition in hemibonded configurations of the radical proves to be responsible for an absorption feature at 230 nm that is strongly shifted with respect to the gas-phase absorption at 307 nm, but this intense feature is substantially diminished in aqueous geometries where the hemibond is absent. Although not yet sufficient to quantitatively establish the population of hemibonded ˙OH(aq), these simulations do suggest that its presence is revealed by the strongly shifted ultraviolet absorption spectrum of the aqueous radical.

Graphical abstract: Role of hemibonding in the structure and ultraviolet spectroscopy of the aqueous hydroxyl radical

Supplementary files

Article information


Submitted
04 Oct 2020
Accepted
11 Nov 2020
First published
12 Nov 2020

Phys. Chem. Chem. Phys., 2020,22, 27829-27844
Article type
Paper

Role of hemibonding in the structure and ultraviolet spectroscopy of the aqueous hydroxyl radical

B. Rana and J. M. Herbert, Phys. Chem. Chem. Phys., 2020, 22, 27829 DOI: 10.1039/D0CP05216G

To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page.

If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given.

If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page.

Read more about how to correctly acknowledge RSC content.


Social activity

Search articles by author

Spotlight

Advertisements