Preprints
https://doi.org/10.5194/acp-2021-424
https://doi.org/10.5194/acp-2021-424

  15 Jun 2021

15 Jun 2021

Review status: this preprint is currently under review for the journal ACP.

Photo-initiated ground state chemistry: How important is it in the atmosphere?

Keiran Nicholas Rowell1,2, Scott Henderson Kable2, and Meredith Jane Trevenar Jordan1 Keiran Nicholas Rowell et al.
  • 1School of Chemistry, University of Sydney, Sydney, Australia
  • 2School of Chemistry, University of New South Wales, Sydney, Australia

Abstract. Carbonyls are among the most abundant volatile organic compounds in the atmosphere. They are central to atmospheric photochemistry as absorption of near-UV radiation by the C=O chromophore can lead to photolysis. If photolysis does not occur on electronic excited states, non-radiative relaxation to the ground state will form carbonyls with extremely high internal energy. These “hot” molecules can access a range of ground state reactions. Up to nine potential ground state reactions are investigated at the B2GP-PLYP-D3/def2-TZVP level of theory for a dataset of 20 representative carbonyls. Almost all are energetically accessible under tropospheric conditions. Comparison with experiment suggests the most significant ground state dissociation pathways will be concerted triple fragmentation in saturated aldehydes, Norrish type III dissociation to form another carbonyl, and H2-loss involving the formyl H atom in aldehydes. Tautomerisation, leading to more reactive unsaturated species, is also predicted to be energetically accessible and is likely to be important when there is no low-energy ground state dissociation pathway, for example in α,β-unsaturated carbonyls and some ketones. The concerted triple fragmentation and H2-loss pathways have immediate atmospheric implication to global H2 production and tautomerisaton has implication to the atmospheric production of organic acids.

Keiran Nicholas Rowell et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2021-424', Anonymous Referee #1, 08 Jul 2021
  • RC2: 'Comment on acp-2021-424', Anonymous Referee #2, 29 Jul 2021
  • AC1: 'Response to Reviewer's Comments on acp-2021-424', Meredith Jordan, 04 Oct 2021

Keiran Nicholas Rowell et al.

Keiran Nicholas Rowell et al.

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Short summary
Sunlight drives chemical reactions in the atmosphere by breaking chemical bonds. Motivated by the knowledge that, if we can better understand the fundamental chemistry, we will be better able to predict atmospheric composition and model any future changes, we use quantum chemistry to investigate new classes of atmospheric reactions. We identify several potentially important reaction classes that will have implications to the atmospheric production of organic acids and molecular hydrogen.
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