Formation and Stabilization of Ground and Excited State Singlet O$_2$ upon Recombination of $^3$P Oxygen on Amorphous Solid Water

TL;DR

This study investigates how oxygen atoms recombine on amorphous solid water to produce stable ground and excited singlet and triplet O$_2$, revealing their relative formation rates and potential impact on cold cloud chemistry.

Contribution

It demonstrates the formation and stabilization of both ground and excited singlet O$_2$ states during recombination on amorphous water, supported by experimental and kinetic modeling.

Findings

Equal proportions of ground and excited singlet and triplet O$_2$ are formed.

Recombination leads to stable species relevant for cold cloud chemistry.

Results align with wavepacket simulation models.

Abstract

The recombination dynamics of $^3$P oxygen atoms on cold amorphous solid water to form triplet and singlet molecular oxygen (O$_2$) is followed under conditions representative for cold clouds. It is found that both, formation of ground state ($X ^3 \Sigma_{g}^{-}$) O$_2$ and molecular oxygen in the two lowest singlet states ($a ^1\Delta_g$ and $b ^1\Sigma_g^+$) is possible and that the species can stabilize. The relative proportions of the species is approximately 1:1:1. These results also agree qualitatively with a kinetic model based on simplified wavepacket simulations. As the chemical reactivity of triplet and singlet O$_2$ is different it is likely that substantial amounts of $a ^1\Delta_g$ and $b ^1\Sigma_g^+$ oxygen influences the chemical evolution of cold clouds.