Basic Atmospheric Chemistry: A Quantum Chemical Study on Hydration of Mesospheric NaOH

Simon Petrie

doi:10.1071/EN04001

RESEARCH ARTICLE

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Basic Atmospheric Chemistry: A Quantum Chemical Study on Hydration of Mesospheric NaOH

Simon Petrie

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Department of Chemistry, the Faculties, Australian National University, Canberra ACT 0200, Australia (e-mail: simon.petrie@anu.edu.au).

Environmental Chemistry 1(1) 35-43 https://doi.org/10.1071/EN04001
Submitted: 3 February 2004 Accepted: 9 March 2004 Published: 30 June 2004

Environmental Context. A natural global layer of sodium atoms exists in the mesosphere, 80–95 km above sea level, where it originates—along with lithium, iron, and calcium—from ablation of meteors. Sodium, as its hydroxide, readily associates with free water to form NaOH·(H₂O)_n clusters. The clusters strongly emit IR radiation and may therefore affect the upper atmosphere’s temperature profile; the clusters are also likely to be a source of nuclei for noctilucent clouds. The same NaOH-based processes may also occur at lower altitudes in the troposphere where water is more abundant than carbon dioxide.

Abstract. The sequential association of water molecules with NaOH, a key upper-atmosphere metal-containing molecule, is investigated using quantum chemical calculations. The first several H₂O–NaOH·(H₂O)_n_–1 bond strengths are sizeable (respectively 82, 70, 56, 42, 42, and 36 kJ mol^–1 according to calculations), suggesting that the termolecular association reactions of NaOH·(H₂O)_n–1 with H₂O may well be efficient upper-atmospheric processes. Such reactions would provide an alternative or additional pathway to the production of hydrated sodium bicarbonate, which has been implicated in the nucleation of noctilucent clouds. The NaOH·(H₂O)_n complexes are also characterized by very large IR intensities across the 3–5 μm wavelength range, suggesting that they may contribute disproportionately to the IR emission profile of the upper atmosphere.

Keywords. : ab initio calculations — atmospheric chemistry — clusters — hydroxides — sodium

Acknowledgements

This work was supported by the allocation of supercomputing resources, housed at the ANU Supercomputing Facility, from the Australian Partnership of Advanced Computing.

References

Basic Atmospheric Chemistry: A Quantum Chemical Study on Hydration of Mesospheric NaOH

Acknowledgements

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