Reactive quenching of NO (A²Σ⁺) with H₂O leads to HONO: a theoretical analysis of the reactive and nonreactive electronic quenching mechanisms

Abstract

In this study, we develop a mechanistic understanding of the pathways for nonreactive and reactive electronic quenching of NO (A2Σ+) with H2O. In doing so, we identify a photochemical mechanism for HONO production in the upper atmosphere.

Theoretical Study of the Photochemical Mechanisms of the Electronic Quenching of NO(A2Σ+) with CH4, CH3OH, and CO2

“…As this occurs, NO develops a partial positive charge and CH 3 OH a partial negative charge, consistent with intermolecular electron transfer. Similar behavior was observed in our previous studies of the NO­( A 2 Σ + ) + CO and NO­( A 2 Σ + ) + H 2 O systems and is consistent with the harpoon mechanism, wherein the formation of a transient ion-pair increases the strength of the intermolecular attractions. ,,− …”

“…As in our previous studies, we employ the equation-of-motion electron attachment coupled-cluster singles and doubles (EOM-EA-CCSD) methodology in this work. , This allows us to use the closed-shell NO + + M reference to avoid the challenges associated with using an open-shell reference. EOM-EA-CCASD will accurately describe all target doublet states of NO + M whose dominant electron configurations can be generated by adding an electron to a virtual orbital of the NO + + M reference.…”

“…As summarized in Figure , our two recent computational studies provide insights into NO­( A 2 Σ + ) + H 2 O and NO­( A 2 Σ + ) + CO electronic quenching mechanisms. , Here, we introduce the notation D 2 to represent the NO­( A 2 Σ + ) + M electronic state, while D 0 and D 1 are associated with NO­( X 2 Π) + M. Note that NO­( X 2 Π) + M is doubly-degenerate at very large intermolecular distances but splits into two low-lying electronic states due to intermolecular interactions with the molecular partner. Figure a shows that the NO + H 2 O and NO + CO intermolecular interactions are attractive for the D 2 state and strongly repulsive for D 1 .…”

“…All energies are reported relative to an optimized geometry on D 2 with an intermolecular distance of 10 Å. Adapted with permission from the American Chemical Society, ref ( 22 ), and the Royal Society of Chemistry, ref ( 23 ).…”

Interplay of Hydrogen, Pnicogen, and Chalcogen Bonding in X(H2O)n=1–5 (X = NO, NO+, and NO–) Complexes: Energetics Insights via a Molecular Tailoring Approach

“…Atomistic-level insights into hydrated NO and identification of the nature of noncovalent interactions among them have received immense attention in recent years. − Several research groups confirmed the hydrogen bond (HB) interaction between neutral NO and water with the help of infrared spectrum, mass spectrometry, and laser techniques. − The potential energy surface of NO­(H 2 O) complexes at the ab initio level was initially reported by Myszkiewicz and Sadlej . Several theoretical analyses, like the quantum theory of atoms in molecules (QTAIM) and natural bond orbital (NBO), were used to characterize and quantify the nature of interactions in the NO­(H 2 O) complex. ,, Despite the importance of NO and water interactions in several research areas, the microhydration of NO has not been explored well at the molecular level.…”