Hydrogen-Bond Scalar Couplings as Covalency-Sensitive NMR Fingerprints of Amorphous Ice

Abstract

Through-hydrogen-bond scalar couplings are attractive NMR observables because they connect high-precision spectroscopy with local hydrogen-bond structure. It is less clear whether they can also report hydrogen-bond covalency in amorphous ice and other frozen or heterogeneous aqueous environments. Here, we combine ab initio molecular dynamics configurations of water, density functional response calculations of indirect nuclear spin–spin couplings, and absolutely localized molecular orbital (ALMO) energy decomposition analysis. Benchmark calculations against SOPPA(CCSD) water-dimer references validate BLYP/pcJ-1 for the through-hydrogen-bond 1h J O–H coupling. The coupling is dominated by the Fermi contact term and therefore follows an approximately exponential distance dependence, but ensemble and vibrational averaging prevent a transferable one-dimensional distance ruler. Extending earlier NMR/ALMO work on liquid water, 1h J O–H correlates with ALMO charge-transfer stabilization and charge-transfer amount. Thus, 1h J O–H is an experimentally accessible, covalency-sensitive fingerprint of hydrogen bonds, provided that geometry and ensemble effects are included explicitly.