Molecular-level insight into uptake of dimethylamine on hydrated nitric acid clusters

Abstract

Mixed nitric acid/water clusters with dimethylamine (DMA) represent a suitable model system for understanding acid–base chemistry in atmospherically relevant clusters. We investigate these clusters in a detailed molecular-beam experiment accompanied by ab initio calculations. The (HNO3)M(H2O)N clusters are produced by supersonic expansion into vacuum and doped by DMA molecules in a pickup process. Two complementary mass spectrometry approaches are employed to analyze the resulting (DMA)K(HNO3)M(H2O)N clusters: (i) electron impact ionization at 70 eV to form positive cluster ions and (ii) low-energy electron attachment at 0–10 eV to form negative clusters. The positive ion spectra contain mainly protonated (DMA)k(HNO3)mH+ clusters with k = m + 1, whereas the negative ones are dominated by (DMA)k(HNO3)mNO3 with mk, followed by (DMA)k(HNO3)mNO2 (m > k) ions with low abundances. These observations are rationalized by our calculations, which exhibit the tendency of the mixed clusters to maximize the number DMA·H+ and NO3 ions in the clusters. In the neutral clusters, this is fulfilled for 1 : 1 ratio of DMA and HNO3, while the positively charged (DMA)k(HNO3)mH+ clusters satisfy this condition for k = m + 1. The protonated clusters always contain the DMA·H+ moiety. For the negatively charged cluster ions, thermochemistry supports the prevailing formation of NO3 and mk ion composition. Furthermore, the NO3-containing cluster ions can form when an electron attaches to the protonated moiety of the DMA·H+⋯NO3 ion pair in the cluster, which leads to H atom evaporation. From the gas phase HNO3 molecule, where NO2 is formed exclusively upon an electron attachment, the tendency to form NO3 increases to hydrated HNO3 clusters, where both NO2 and NO3 ions are generated in approximately equal abundances, to the DMA doped clusters, where NO3 strongly prevails NO2.

Graphical abstract: Molecular-level insight into uptake of dimethylamine on hydrated nitric acid clusters

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Article information

Article type
Paper
Submitted
27 Jul 2022
Accepted
19 Aug 2022
First published
26 Aug 2022
This article is Open Access
Creative Commons BY-NC license

Environ. Sci.: Atmos., 2022, Advance Article

Molecular-level insight into uptake of dimethylamine on hydrated nitric acid clusters

A. Pysanenko, K. Fárníková, J. Lengyel, E. Pluhařová and M. Fárník, Environ. Sci.: Atmos., 2022, Advance Article , DOI: 10.1039/D2EA00094F

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