Surface structure of water from soft X-ray second harmonic generation

Hoffman, David J. [SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States)] (ORCID:0000000185187676); Devlin, Shane W. [University of California, Berkeley, CA (United States); Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States). Advanced Light Source (ALS); Univ. of Nevada, Las Vegas, NV (United States)]; Garratt, Douglas [SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States)] (ORCID:0000000286379984); Jamnuch, Sasawat [Theiss Research, La Jolla, CA (United States); National Inst. of Standards and Technology (NIST), Gaithersburg, MD (United States)]; Spies, Jacob A. [University of California, Berkeley, CA (United States); Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)]; Nebgen, Bailey R. [University of California, Berkeley, CA (United States); Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)] (ORCID:0000000310067092); Schacher, Daniel [Univ. of Nevada, Las Vegas, NV (United States)] (ORCID:0000000240956635); Do, Alexandria [Univ. of California, San Diego, La Jolla, CA (United States)]; Bernal, Franky [University of California, Berkeley, CA (United States); Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)] (ORCID:0000000166536367); Riffe, Erika J. [University of California, Berkeley, CA (United States); Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)] (ORCID:000000027369562X); Kunnus, Kristjan [SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States)]; Hampton, Christina Y. [SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States)]; Duris, Joseph [SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States)] (ORCID:0000000299301166); Cesar, David [SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States)]; Sudar, Nicholas [SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States)]; Dakovski, Georgi L. [SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States)]; Drisdell, Walter S. [Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)] (ORCID:0000000286934562); Lawler, Keith V. [Univ. of Nevada, Las Vegas, NV (United States)] (ORCID:0000000310875815); Marinelli, Agostino [SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States)] (ORCID:0000000272484652); Zuerch, Michael W. [University of California, Berkeley, CA (United States); Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)] (ORCID:0000000151512119); Saykally, Richard J. [University of California, Berkeley, CA (United States); Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)]; Schwartz, Craig P. [Univ. of Nevada, Las Vegas, NV (United States)] (ORCID:0000000241492684); Pascal, Tod A. [Univ. of California, San Diego, La Jolla, CA (United States)] (ORCID:0000000320961143); Koralek, Jake D. [SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States)] (ORCID:0000000182890497)

doi:10.1038/s41467-025-65514-4

DOE OSTI · 3024436

Surface structure of water from soft X-ray second harmonic generation

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Abstract

The microscopic structure of water’s surface is crucial to many natural and industrial processes, but studying its hydrogen bond (H-bond) network directly remains challenging due to the required interfacial sensitivity of experimental techniques. By leveraging advances in flat liquid sheet microjets and terawatt-scale attosecond soft X-ray pulses from the LCLS X-ray free electron laser, we employed soft X-ray second harmonic generation (SXSHG) spectroscopy to examine the liquid water/vapor interface. SXSHG combines the elemental selectivity of X-ray spectroscopies with the surface selectivity of SHG and gives access to the electronic structure of interfacial species. Here, we show the SXSHG spectrum differs from bulk water’s X-ray absorption, with its peak shifted several eV, indicating a vastly different electronic environment at the interface as compared to the bulk. First-principles electronic structure calculations show the signal is highly sensitive to H-bond interactions, such as water molecules accepting a single H-bond, which are surface abundant.

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Hoffman, David J. [SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States)] (ORCID:0000000185187676), Devlin, Shane W. [University of California, Berkeley, CA (United States); Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States). Advanced Light Source (ALS); Univ. of Nevada, Las Vegas, NV (United States)], Garratt, Douglas [SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States)] (ORCID:0000000286379984), Jamnuch, Sasawat [Theiss Research, La Jolla, CA (United States); National Inst. of Standards and Technology (NIST), Gaithersburg, MD (United States)], Spies, Jacob A. [University of California, Berkeley, CA (United States); Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)], Nebgen, Bailey R. [University of California, Berkeley, CA (United States); Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)] (ORCID:0000000310067092), Schacher, Daniel [Univ. of Nevada, Las Vegas, NV (United States)] (ORCID:0000000240956635), Do, Alexandria [Univ. of California, San Diego, La Jolla, CA (United States)], Bernal, Franky [University of California, Berkeley, CA (United States); Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)] (ORCID:0000000166536367), Riffe, Erika J. [University of California, Berkeley, CA (United States); Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)] (ORCID:000000027369562X), Kunnus, Kristjan [SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States)], Hampton, Christina Y. [SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States)], Duris, Joseph [SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States)] (ORCID:0000000299301166), Cesar, David [SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States)], Sudar, Nicholas [SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States)], Dakovski, Georgi L. [SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States)], Drisdell, Walter S. [Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)] (ORCID:0000000286934562), Lawler, Keith V. [Univ. of Nevada, Las Vegas, NV (United States)] (ORCID:0000000310875815), Marinelli, Agostino [SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States)] (ORCID:0000000272484652), Zuerch, Michael W. [University of California, Berkeley, CA (United States); Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)] (ORCID:0000000151512119), Saykally, Richard J. [University of California, Berkeley, CA (United States); Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)], Schwartz, Craig P. [Univ. of Nevada, Las Vegas, NV (United States)] (ORCID:0000000241492684), Pascal, Tod A. [Univ. of California, San Diego, La Jolla, CA (United States)] (ORCID:0000000320961143), Koralek, Jake D. [SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States)] (ORCID:0000000182890497). 2025-11-26. Surface structure of water from soft X-ray second harmonic generation. https://doi.org/10.1038/s41467-025-65514-4

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