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Theodore S. Dibble @ted-dibble.bsky.social · 27/07/2026

This work was carried out by my Ph.D. student, Darshi T. Hewa Edirappulige, with help from my postdoc Pedro J. Castro. The photo shows Darshi with her ACS PHYS poster award from 2025. Darshi will defend her thesis next month. Anyone looking for a sharp computational chemist? 6/6

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Theodore S. Dibble @ted-dibble.bsky.social · 27/07/2026

Our conclusion: The reported loss of Hg(0) is best explained by surface-reactions, not a gas-phase reaction. The gas-phase Hg(0)+O₃ reaction appears irrelevant in the laboratory and in the atmosphere. Interested in your feedback! DOI: 10.1021/acs.jpca.6c02693 5/6

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Theodore S. Dibble @ted-dibble.bsky.social · 27/07/2026

The other hypothesized product was OHgOO. Production of this diradicaloid from Hg(0) + O3 is endothermic by > 21 kcal/mole. Given this, a gas-phase reaction would have an observed rate at least 10 billion times lower than reported. 4/6

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Theodore S. Dibble @ted-dibble.bsky.social · 27/07/2026

To test the possibility of a direct Hg(0) + O3 reaction, we used high-level quantum chemistry to examine two hypothesized reaction products. One was a cyclic HgO3, which collapses to a Hg–O₃ van der Waals complex. This is unstable and does not lead to a chemical reaction. 3/6

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Theodore S. Dibble @ted-dibble.bsky.social · 27/07/2026

Some modelers insisted they needed one-step oxidation by OH and/or O3 to match field observations. Three years ago we showed that O3 and OH, together, can oxidize Hg(0) in two steps (DOI: 10.1021/acs.jpca.2c04364). But this doesn’t rule out a direct Hg(0) + O3 reaction! 2/6

Text “Two-step reaction mechanism” followed on subsequent line by the reaction OH + Hg reversibly forming HOHg radical. The next line has the reaction of HOHg radical with ozone to form HOHgO and molecular oxygen.

Two graphs next to each other, one labeled March 4, 2010 and the other labeled July 1, 2010. The x-axes are labeled “Fraction HOHg radical making Hg(II)” and run from zero to one. The y-axes are labeled altitude and run from 0 km to 18 km. Both graphs have black lines labeled “without ozone” and blue lines labeled “with ozone”. Both lines labeled “without ozone” start at 0.2 or below and decay to zero in going from 0 to 2 km and stay low thereafter. The lines marked “with ozone” start at 0.45 or higher and approach 1.0 at 6-8 km.

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Theodore S. Dibble @ted-dibble.bsky.social · 27/07/2026

Many models of atmospheric mercury include a GAS-PHASE Hg(0) + O3 reaction. But the observed products are solids (see image from PCCP 2008, by Pal and Ariya), suggesting reaction on the reactor walls. New paper: 10.1021/acs.jpca.6c02693 🧵 1/6

$Electron micrograph of about 7 quasi-spherical balls, which turns into a quasi-fractal assemblage of hundreds of balls when at 50% relative humidity$

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Theodore S. Dibble @ted-dibble.bsky.social · 27/07/2026

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Theodore S. Dibble @ted-dibble.bsky.social · 27/07/2026

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Theodore S. Dibble @ted-dibble.bsky.social · 22/02/2026

My PhD student Darshi is first author of the paper refuting the proposed importance of NO3-initiated oxidation of Hg(0) in the gas phase. This paper combines advanced quantum chemical calculations, kinetic analysis, and global atmospheric modeling, DOI: 10.1021/acsearthspacechem.5c00382

Graph of Hg-X bond energy (in kcal/mole) versus radicals X, starting with F, Cl, Br, and I, then OH and NO3. Subtitle: Ability of radicals to initiate oxidation of Hg(0). F and Cl are in a box labeled "[F] and [Cl] too low" and I, OH, and NO3 are in a box labeled "bonds too weak".

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Theodore S. Dibble @ted-dibble.bsky.social · 14/12/2025

I look forward to seeing posters in #RSCEnv and #RSCPhys and interacting with the presenters at #RSCPoster 2026. This 24-hour online event offers cash prized in each of 15 areas of chemistry. To Register, and for more information, go to rsc.li/4ppNbyo

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Theodore S. Dibble @ted-dibble.bsky.social · 17/07/2025

To overcome racial inequality, we must confront our history. @eji.org See t.co/1NMZDV9weO for the history of this injustice from 1954 that mirrors what's happening today

Black and white photo of Hispanic-looking people standing in a large cage.

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Theodore S. Dibble @ted-dibble.bsky.social · 29/01/2025

I’m looking for new PhD students wanting to use computational chemistry to study atmospheric reactions. Topics: Hg redox reactions at surfaces. AI to study how hydrogen bonds (R=O--HO• and RO(H)--HO) affects kinetics of H-abstraction. See www.esf.edu/faculty/dibble or tsdibble@esf.edu

Map of the world color-coded by the percent of HgOH going on to make HG(II) compounds. The Schrodinger equation is depicted below Africa.

BrHgOH molecule on a layer of water molecules (meant to represent the top layer of the surface of ice).

OH radical donating a hydrogen bond to acetaldehyde (ethanal).

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