Nuclear Magnetic Resonance Spectroscopy as a Dynamical Structural Probe of Hydrogen under High Pressure

Abstract

An unambiguous crystallographic structure solution for the observed phases II-VI of high pressure hydrogen does not exist due to the failure of standard structural probes at extreme pressure. In this work we propose that nuclear magnetic resonance spectroscopy provides a complementary structural probe for high pressure hydrogen. We show that the best structural models available for phases II, III, and IV of high pressure hydrogen exhibit markedly distinct nuclear magnetic resonance spectra which could therefore be used to discriminate amongst them. As an example, we demonstrate how nuclear magnetic resonance spectroscopy could be used to establish whether phase III exhibits polymorphism. Our calculations also reveal a strong renormalisation of the nuclear magnetic resonance response in hydrogen arising from quantum fluctuations, as well as a strong isotope effect. As the experimental techniques develop, nuclear magnetic resonance spectroscopy can be expected to become a useful complementary structural probe in high pressure experiments.

Unconventional phase III of high-pressure solid hydrogen

“…The DMC phase diagram with an optimised exchange weight indicates that the phase III of solid hydrogen is polymorphic. Our prediction on polymorphic nature of the phase III agrees with recent nuclear magnetic resonance spectroscopy observation 45 . A very recent experimental observation shows a first order phase transition near 425 GPa from insulator molecular phase to metallic hydrogen 46 .…”

“…Our DMC enthalpy-pressure phase diagram which is obtained at the minimised α indicates that the phase III of solid hydrogen adopts two structures of P 6 1 22, which is stable below ∼210 GPa, and the C2/c which is stable at pressures above ∼ 210 GPa. We predict that the phase III exhibits polymorphism which is also predicted recently by nuclear magnetic resonance spectroscopy 45 .…”

High-Pressure NMR Enabled by Diamond Nitrogen-Vacancy Centers

“…On the other hand, NMR is an important spectrum methods to reveal local electronic, chemical and structural information. High-pressure NMR offers unique opportunities to study dynamical structure of hydrogen and hydrides [6,7], phase transitions of metal and superconductor [8], and protein folding process [9], to name a few.…”

In-situ High Pressure Nuclear Magnetic Resonance Crystallography

“…(i): further improvements of the sensitivity for small sample fractions in the 2D spectra (ii): the combination of high-P NMR with structure search calculations as suggested by Monserrat et al62 …”