Freiburg 2024 – wissenschaftliches Programm
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MO: Fachverband Molekülphysik
MO 26: Cluster
MO 26.4: Vortrag
Freitag, 15. März 2024, 15:15–15:30, HS 3042
Mass Spectrometry Analysis of Binary Formic Acid-Water Clusters upon Collision with Electrons — •Kevin Li1, Jozef Ďurana2, Michal Fárník2, and Jozef Lengyel1 — 1TU München, Garching, Germany — 2Czech Academy of Sciences, Prague, Czechia
A significant portion of atmospheric particles is formed through the nucleation and condensation of precursor gases in a process known as new particle formation (NPF), where organic acids play a crucial role as key precursor gases that enhance nucleation rates. It is, therefore, essential to understand the collisions of gas-phase molecules with clusters and to establish protocols for analyzing these particles using mass spectrometry. This is particularly important for hydrogen-bonded particles, as they frequently undergo extensive fragmentation upon ionization. In our experiments, mixed clusters of formic acid and water were produced in supersonic expansion and subsequently investigated by mass spectrometry using different ionization methods, namely (i) the electron ionization at 70 eV (EI) and (ii) the low energy electron attachment (EA). While for positive ionization mainly protonated clusters (H2O)n/(HCOOH)m/H+ were detected, negative mass spectroscopy revealed two species, (H2O)n/(HCOOH)-m and (H2O)n/(HCOOH)m-1/HCOO-. Both techniques indicate that higher water content in the solution results in clusters with a high degree of hydration and fewer formic acid molecules. Additionally, the fraction of the two anionic species is influenced by cluster size, level of hydration, and electron energy. The detailed behavior of ionization will be discussed in the presentation.
Keywords: molecular clusters; cluster formation; hydrogen bonding; mass spectrometry; molecule-cluster collision