Table 1 Number of water molecules (n) contributing to the observed bands, determined from the fit of the pressure-dependent spectroscopic signal to Poisson distributions.

The pickup curves were recorded at a particular on-resonance frequency. See also the “Ionization mechanism of pure water and mixed HCl-water aggregates” and “The umbrella motion of hydronium: Parent cluster size determination” sections in the Supplementary Materials.

Resonance frequency
(cm−1)
Mass channel
(atomic mass units)
n
1320414
1320614
1400614
1250815