Infrared spectroscopy of solid mixed ammonia–water and acetylene–water aerosol particles

Abstract

Mixed water aerosols are important components of planetary and lunar atmospheres. In this work, we use rapid-scan Fourier transform infrared (IR) spectroscopy to study solid ammonia–water and acetylene–water aerosol particles formed in a bath gas cooling cell at 78 K. With this set-up, we record time-dependent extinction spectra of particle ensembles in the mid-IR to monitor changes to the internal structure of the aerosol particles. Both ammonia–water and acetylene–water were found to form molecularly mixed structures. The mixing is observed by monitoring the profile for the ammonia ν₂ band and the acetylene ν₅ band, both of which are sensitive to particle properties. Depending on the injection conditions, the mixed particles form either immediately after sample injection or after a short mixing period of several tens of minutes. We confirm the formation of mixed particles by comparing the experimental spectra with spectra calculated with the vibrational exciton model.

Keywords:

• vibrational exciton model
• molecular ices
• solid-state diffusion

Acknowledgements

We would like to thank Dr Kerry Knox and Dr Kathrin Lang for assistance with experiments. Advanced computing resources were provided by West-Grid and Compute/Calcul Canada.

Additional information

Funding

This work was funded by the ETH Zürich and the Swiss National Science Foundation (SNF) [grant number 200021_146368/1]; and Merrill Isenor received funding from an NSERC postgraduate scholarship and a Walter C. Sumner Memorial Fellowship.