An experimental and computational view of the photoionization of diol-water clusters

Anna Wannenmacher; Wenchao Lu; Chandika Amarasinghe; Frank Cerasoli; Davide Donadio; Musahid Ahmed

doi:10.1063/5.0198162

An experimental and computational view of the photoionization of diol-water clusters

J Chem Phys. 2024 Apr 14;160(14):144303. doi: 10.1063/5.0198162.

Authors

Anna Wannenmacher^{1

2}, Wenchao Lu¹, Chandika Amarasinghe¹, Frank Cerasoli², Davide Donadio², Musahid Ahmed¹

Affiliations

¹ Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
² Department of Chemistry, University of California, Davis, California 95616, USA.

PMID: 38591680
DOI: 10.1063/5.0198162

Abstract

In the interstellar medium, diols and other prebiotic molecules adsorb onto icy mantles surrounding dust grains. Water in the ice may affect the reactivity and photoionization of these diols. Ethylene glycol (EG), 1,2-propylene glycol, and 1,3-propylene glycol clusters with water clusters were used as a proxy to study these interactions. The diol-water clusters were generated in a continuous supersonic molecular beam, photoionized by synchrotron-based vacuum ultraviolet light from the Advanced Light Source, and subsequently detected by reflectron time-of-flight mass spectrometry. The appearance energies for the detected clusters were determined from the mass spectra, collected at increasing photon energy. Clusters of both diol fragments and unfragmented diols with water were detected. The lowest energy geometry optimized conformers for the observed EG-water clusters and EG fragment-water clusters have been visualized using density functional theory (DFT), providing insight into hydrogen bonding networks and how these affect fragmentation and appearance energy. As the number of water molecules clustered around EG fragments (m/z 31 and 32) increased, the appearance energy for the cluster decreased, indicating a stabilization by water. This trend was supported by DFT calculations. Fragment clusters from 1,2-propylene glycol exhibited a similar trend, but with a smaller energy decrease, and no trend was observed from 1,3-propylene glycol. We discuss and suggest that the reactivity and photoionization of diols in the presence of water depend on the size of the diol, the location of the hydroxyl group, and the number of waters clustered around the diol.