Ted Hullar^1*, Theo Tran^1*, Zekun Chen^2*, Fernanda C. Bononi^2*, Oliver Palmer^1*, Davide Donadio^2*, Cort Anastasio^1*

1 Department of Land, Air and Water Resources, University of California, Davis, CA 95616, USA

2 Department of Chemistry, University of California, Davis, CA 95616, USA

* Corresponding authors emails: thullar@ucdavis.edu, cuctran@ucdavis.edu, zkuchen@ucdavis.edu, fcbononi@ucdavis.edu, otpalmer@ucdavis.edu, ddonadio@ucdavis.edu, canastasio@ucdavis.edu

DOI10.24435/materialscloud:q7-yg [version v1]

Publication date: Apr 20, 2022

How to cite this record

Ted Hullar, Theo Tran, Zekun Chen, Fernanda C. Bononi, Oliver Palmer, Davide Donadio, Cort Anastasio, Enhanced photodegradation of dimethoxybenzene isomers in/on ice compared to in aqueous solution, Materials Cloud Archive 2022.54 (2022), https://doi.org/10.24435/materialscloud:q7-yg

Description

Photochemical reactions of contaminants in snow and ice can be important sources and sinks for various organic and inorganic compounds. Snow contaminants can be found in the bulk ice matrix, in internal liquid-like regions (LLRs), or in quasi-liquid layers (QLLs) at the air-ice interface, where they can readily exchange with the firn air. Some studies have reported that direct photochemical reactions occur faster in LLRs and QLLs than in aqueous solution, while others have found similar rates. Here, we measure the photodegradation rate constants of the three dimethoxybenzene isomers under varying experimental conditions, including in aqueous solution, in LLRs, and at the air-ice interface of nature-identical snow. Relative to aqueous solution, we find modest photodegradation enhancements (3- and 6-fold) in LLRs for two of the isomers, and larger enhancements (15- to 30-fold) at the air-ice interface for all three isomers. We use computational modeling to assess the impact of light absorbance changes on photodegradation rate enhancements at the interface. We find small (2–5 nm) bathochromic (red) absorbance shifts at the interface relative to in solution, which increases light absorption, but this factor only accounts for less than 50 % of the measured rate constant enhancements. The major factor responsible for photodegradation rate enhancements at the air-ice interface appears to be more efficient photodecay: estimated dimethoxybenzene quantum yields are 6- to 24-fold larger at the interface compared to in aqueous solution and account for the majority (51–96 %) of the observed enhancements. Using a hypothetical model compound with an assumed Gaussian-shaped absorbance peak, we find that a shift in the peak to higher or lower wavelengths can have a minor to substantial impact on photodecay rate constants, depending on the original location of the peak and the magnitude of the shift. Changes in other peak properties at the air-ice interface, such as peak width and height (i.e., molar absorptivity) can also impact rates of light absorption and direct photodecay.

Materials Cloud sections using this data

Files

File name	Size	Description
abs_ML.zip MD5md5:cc8d7eede5cb28561051e6b4e809d4d2	8.1 MiB	Molecular geometries sampled from AIMD for three DMB isomers in solution and at air-ice interface.
classical_MD.zip MD5md5:57bf08e233828e40ccc59fd23a1b242d	560.5 KiB	Production: LAMMPS files used for production runs on the ice surface for 2-DMB, 3-DMB and 4-DMB
FPMD.zip MD5md5:0cdc2c3b4836ba8b89c2e021b2900028	421.4 KiB	CP2K input: CP2K input files used for First-principles MD simulations in solution and on the ice surface for 2-DMB, 3-DMB and 4-DMB.

License

Files and data are licensed under the terms of the following license: Creative Commons Attribution 4.0 International.
Metadata, except for email addresses, are licensed under the Creative Commons Attribution Share-Alike 4.0 International license.

External references

Keywords

absorption spectra ice dimethoxybenzene