2025/10/24 by Ltaief, Ltaief Ben, Sishodia, Keshav, Richter, Robert +6
#Atomic and Molecular Clusters (physics.atm-clus) #Chemical Physics (physics.chem-ph) #FOS: Physical sciences
paper · doi:10.48550/arxiv.2510.22000
The microhydration of rock salt (NaCl) molecules was investigated using high-resolution Penning ionization electron spectroscopy (PIES) in helium nanodroplets. Although model calculations predict that NaCl molecules are fully submerged inside the droplets, PIES of NaCl are highly resolved, in stark contrast to other molecular species. Co-doping the droplets with a controlled number of n=5--10 water molecules leads to efficient quenching of the NaCl Penning ionization signal and to its full suppression for n\gtrsim 30. Accompanying density-functional theory (DFT) and force field calculations reveal a transition from contact ion pair structures to solvent-separated ion pairs at n=12--15. However, it takes n≈ 17 water molecules to form a complete solvation shell around the Cl- anion and as many as n≈ 34 to fully hydrate the Na+ cation, thus the entire NaCl molecule, which rationalizes the experimental findings.