A new study from our group, carried out with collaborators at SLAC National Accelerator Laboratory, UC Berkeley, LBNL, UNLV, and UC San Diego demonstrates how soft X-ray second harmonic generation can directly probe the hydrogen-bonding environment at the liquid water surface. Using flat liquid-sheet microjets and terawatt-scale attosecond soft-X-ray pulses from LCLS, the team measured SXSHG from the water/vapor interface and observed a spectrum that is markedly shifted relative to bulk X-ray absorption, revealing a distinct interfacial electronic structure. First-principles calculations trace this sensitivity to specific H-bond motifs—particularly singly H-bond–accepting molecules that are enriched at the surface. This work establishes SXSHG as a powerful element- and interface-selective probe of aqueous interfacial structure.
From our group Jacob and Bailey have contributed to this research. The collaboration has largely been assembled from the California Interfacial Science Institute (CISI). The experiments were conducted at the LCLS Free Electron Laser at SLAC National Accelerator Laboratory.


The paper is now online with open access at Nature Communications:
https://www.nature.com/articles/s41467-025-65514-4