Science Advances

Supplementary Materials

This PDF file includes:

  • Section S1. Experimental design and additional results
  • Section S2. Simulation methods and additional results
  • Fig. S1. Details of the second vacuum chamber.
  • Fig. S2. Variation of ion current at m/z = 36 with HCl partial pressure in cell 1.
  • Fig. S3. Dependence of the ion current upon water partial pressure as detected on m/z = 41, 61, and 81.
  • Fig. S4. Reference ion current, as a function of H218O partial pressure, detected at mass channels m/z = 41, 61, and 81.
  • Fig. S5. Variation of the spectroscopic signal (red dots) as a function of H218O partial pressure for different mass channels and frequencies.
  • Fig. S6. Poisson fit assuming a superposition of two Poisson distributions for pickup of (H2O)4 and (H2O)5.
  • Fig. S7. Relevant structures of the HCl(H2O)4 cluster as well as that of the Eigen complex, (H3O)+(H2O)3, all optimized using BLYP.
  • Fig. S8. Relevant structures of the HCl(H2O)5 cluster all optimized using BLYP.
  • Fig. S9. Quantum O─H distance distribution functions of the three protons and the oxygen within the hydronium moiety of the CIP5 (top) and SIP5 (bottom) conformers at 1.25 K.
  • Fig. S10. Mechanism leading to the formation of CIP5 after the aggregation of the fifth water molecule with the HCl(H2O)4 SIP C3 conformer in terms of representative snapshots sampled from the ab initio aggregation simulations.
  • Fig. S11. Mechanism leading to the formation of SIP5 (right) via attachment of the fifth water molecule to the Cl site of the SIP C1 conformer (left) in terms of representative snapshots sampled from the ab initio aggregation simulations.
  • Fig. S12. Mechanism leading to the formation of the cyclic UD structure (bottom left) after the aggregation of the HCl molecule with the cyclic water tetramer (H2O)4 has generated the AG structure (top left) in terms of representative snapshots sampled from the ab initio aggregation simulations.
  • Fig. S13. Alternative mechanism leading to the formation of the cyclic UD structure (bottom left) after the aggregation of the HCl molecule with the cyclic water tetramer (H2O)4 has generated the AG structure (top left) in terms of representative snapshots sampled from the ab initio aggregation simulations.
  • Table S1. Relative electronic energy (without inclusion of zero-point energy correction), dipole moment, and (unscaled harmonic) frequency of the hindered umbrella mode of the hydronium moiety, H3O+, in case of ion pair structures for the most relevant HCl(H2O)n isomers with n = 4 and 5, based on optimized MP2 and BLYP structures.
  • Table S2. Aggregation simulations of SIP + H2O with initial NVT electrostatic steering alignment of the water molecule.
  • Table S3. Aggregation simulations of SIP + H2O with the water molecule in random orientations and positions around the center of the SIP cluster.
  • Table S4. Aggregation simulations of the cyclic (H2O)4 cluster with an HCl molecule using three different classes of initial conditions, using different cluster-molecule distances (d), relative velocities (v), and harmonic constants (k), as specified.
  • References (53, 54)

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