Abstract
In this work, an investigation of supercritical water is presented combining inelastic and deep inelastic neutron scattering experiments and molecular dynamics simulations based on a machine-learned potential of ab initio quality. The local hydrogen dynamics is investigated at 250 bar and in the temperature range of 553-823 K, covering the evolution from subcritical liquid to supercritical gas-like water. The evolution of libration, bending, and stretching motions in the vibrational density of states is studied, analyzing the spectral features by a mode decomposition. Moreover, the hydrogen nuclear momentum distribution is measured, and its anisotropy is probed experimentally. It is shown that hydrogen bonds survive up to the higher temperatures investigated, and we discuss our results in the framework of the coupling between intramolecular modes and intermolecular librations. Results show that the local potential affecting hydrogen becomes less anisotropic within the molecular plane in the supercritical phase, and we attribute this result to the presence of more distorted hydrogen bonds.
| Original language | English |
|---|---|
| Pages (from-to) | 9461-9467 |
| Number of pages | 7 |
| Journal | Journal of Physical Chemistry Letters |
| Volume | 11 |
| Issue number | 21 |
| DOIs | |
| State | Published - Nov 5 2020 |
Funding
The authors gratefully acknowledge the financial support of Regione Lazio concerning collaboration in scientific research at ISIS@MACH Research Infrastructure (IR approved by Giunta Regionale no. G10795, 7 August 2019 published by BURL no. 69 27 August 2019) and at the ISIS Neutron and Muon Source (U.K.) of Science and Technology Facilities Council (STFC); the financial support of Consiglio Nazionale delle Ricerche within CNR-STFC Agreement 2014-2020 (N 3420), concerning collaboration in scientific research at the ISIS Neutron and Muon Source (U.K.) of Science and Technology Facilities Council (STFC), is gratefully acknowledged. M.F.C.A., H.-Y.K., and R.C. gratefully acknowledge support from the U.S. Department of Energy (DOE) under Grant No. DE-SC0019394. The work at Spallation Neutron Source was supported by the Scientific User Facility Division, Office of Basic Energy Sciences, (U.S.) Department of Energy (DOE). We thank Prof. C.-K. Loong for very useful discussions. We also thank A. Seel for help during the measurements on the VESUVIO spectrometer; Justin R. Carmichael for the design of the sample container; and John Wenzel, Saad R. Elorfi, and Todd E. Sherline for helping with the experiment on the SEQUOIA spectrometer. This research used resources of the National Energy Research Scientific Computing (NERSC) Center, which is supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. Additional resources were provided by the Terascale Infrastructure for Ground-breaking Research in Science and Engineering (TIGRESS) High Performance Computing Center and Visualization Laboratory at Princeton University.
| Funders | Funder number |
|---|---|
| CNR-STFC | N 3420 |
| ISIS Neutron and Muon Source (U.K.) of Science and Technology Facilities Council | |
| U.S. Department of Energy | DE-SC0019394 |
| Office of Science | DE-AC02-05CH11231 |
| Basic Energy Sciences | |
| Science and Technology Facilities Council | |
| Consiglio Nazionale delle Ricerche | |
| Regione Lazio | G10795 |