Structure and Spectroscopy of Criegee Intermediates in Gas- and Aqueous Environments

TL;DR

This study investigates the behavior and spectroscopy of Criegee intermediates in various environments, revealing diffusion characteristics and spectral shifts that enhance understanding of their roles in atmospheric and aqueous chemistry.

Contribution

The paper provides new insights into the diffusion and spectral properties of Criegee intermediates in gas, water droplet, and solid water environments using validated energy functions.

Findings

Facile diffusion of CIs in water droplets.

No surface diffusion of CIs on amorphous solid water at 50 K.

Spectral shifts of CIs in aqueous environments are consistent with Stark effects.

Abstract

The dynamics and spectroscopy of the small (H$_2$COO) and large (CH$_3$CHOO) Criegee intermediates (CIs) in the gas phase, inside/on water droplets, on amorphous solid water (ASW) and in bulk water are investigated using validated energy functions. For both species, facile diffusion between surface and inside positions for water droplets are found whereas on amorphous solid water at low temperatures (50 K) no surface diffusion is observed on the multiple-nanosecond time scale. This is at variance with other species, such as CO or NO on ASW. The infrared spectroscopy of both CIs in contact with an aqueous environment leads to shifts of the spectral features on the order of a few to a few tens of cm$^{-1}$, depending on the vibrational mode considered. This is consistent with Stark-induced spectral shifts for small molecules in protein environments. However, the spectroscopy of both CIs in contact with water droplets does not depend on the positioning relative to the droplet (inside vs. surface).