1b1 splitting in the X-ray emission spectrum of liquid water is dominated by ultrafast dissociation

15 September 2023, Version 1
This content is a preprint and has not undergone peer review at the time of posting.


The 1b1 splitting observed in the K-edge non-resonant X-ray emission spectrum (XES) of liquid water has been a subject of intense debate. Some argue that it represents two distinct structural motifs, while others suggest that it is evidence of ultrafast dissociation within the core-hole lifetime. In this study, we use a theoretical approach to provide a nearly quantitative description of both non-resonant and pre-edge resonant XES. Our theoretical predictions indicate that the 1b1 splitting arises due to ultrafast dissociation, with the dynamics of this process dependent on the X-ray absorption energy. For non-resonant radiation, hydrogen is ejected as H+, while for pre-edge resonant radiation it is ejected as a neutral atom. This leads to near-dissociation for non-resonant radiation, as ~ 20% of all core-ionized molecules do not dissociate and dissociated protons still remain in close proximity to the parent hydroxyl fragment. In contrast, for pre-edge radiation, all core-excited molecules dissociate and the neutral H atom moves further away from the hydroxyl fragment, completely leaving the first solvation shell in most cases. Our simulations also predict the observed isotope effects in both non-resonant and pre-edge resonant XES and reveal that the so-called lower-energy 1b1 peak in the non-resonant XES is primarily of 3a1 symmetry. Additionally, we found that hydrogen bonding plays a significant role in explaining the XES behavior across different temperatures and phases.


liquid water
ultrafast dissociation
hydrogen bonding
core hole
peak splitting
orbital symmetry

Supplementary materials

Supplementary Material
The PDF file contains the following sections: 1) Liquid-phase simulations of pure H2O and D2O; 2) Distribution of hydrogen-bonding in the initial structures used in the core-ionized and core-excited simulations; 3) O-H dissociation in core-ionized and core-excited simulations; 4) Protocol to identify orbital symmetry; 5) Core-hole dynamical effects in the X-ray emission spectrum with emphasis on orbital symmetry; 6) Time-averaged X-ray emission spectrum with emphasis on orbital symmetry; 7) Core-hole dynamical effects in the X-ray emission spectrum with emphasis on hydrogen-bonding environment; 8) X-ray emission spectrum predictions with EOM-IP-CCSD; 9) Non-resonant 1b1' peak gains intensity as proton is transferred from core-ionized water to the first solvation shell; 10) X-ray emission spectrum with different core-hole lifetimes; 11) Computational estimates for core-hole lifetimes from Auger decay rates in the gas-phase; 12) Generation of core-ionized and core-excited states.

Supplementary weblinks


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