Stability and Structure of Potentially Atmospherically Relevant Glycine Ammonium Bisulfate Clusters

12 March 2024, Version 2
This content is a preprint and has not undergone peer review at the time of posting.


New particle formation (NPF) is the process by which trace atmospheric acids and bases cluster and grow into particles that ultimately impact climate. Sulfuric acid concentration drives NPF, but nitrogen-containing bases promote the formation of more stable clusters via salt bridge formation. Recent computational efforts have suggested that amino acids can enhance NPF, predicting that they can stabilize new particles via multiple protonation sites, but there has yet to be experimental validation of these predictions. We used mass spectrometry and infrared spectroscopy to study the structure and stability of cationic clusters composed of glycine, sulfuric acid, and ammonia. When collisionally activated, clusters were significantly more likely to eliminate ammonia or sulfuric acid than glycine, while quantum chemical calculations predicted lower binding free energies for ammonia but similar binding free energies for glycine and sulfuric acid. These calculations predicted several low-energy structures, so we compared experimental and computed vibrational spectra to attempt to validate the computationally-predicted minimum energy structure. Unambiguous identification of the experimental structure by comparison to these calculations was made difficult by the complexity of the experimental spectra and the fact that the identity of the computed lowest-energy structure depended strongly on temperature. If their vapors are present, amino acids are likely to be enriched in new particles by displacing more weakly-bound ammonia, similar to the behavior of other atmospheric amines. The carboxylic acid groups were found to preferentially interact with other carboxylic acids, suggesting incipient organic/inorganic phase separation even at these small sizes.


New Particle Formation
Amino Acid
IR Spectroscopy
Collision Induced Dissociation
Free Energy

Supplementary materials

Supplemental Information - Stability and Structure of Potentially Atmospherically Relevant Glycine Ammonium Bisulfate Clusters
This is the supporting information for the working paper titled "Stability and Structure of Potentially Atmospherically Relevant Glycine Ammonium Bisulfate Clusters". This document includes relevant mass spectra, gas phase IR spectra, a comparison of structures across temperatures and the method used for computing free energies for removing specific cluster components and as well as the method used to compute the Boltzmann population of isomers.


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