Nuclear spin conversion of water inside fullerene cages detected by low-temperature nuclear magnetic resonance

Abstract

Articles you may be interested in 194306 (2014) Nuclear spin conversion of water inside fullerene cages detected by low-temperature nuclear magnetic resonance The water-endofullerene H 2 O@C 60 provides a unique chemical system in which freely rotating water molecules are confined inside homogeneous and symmetrical carbon cages. The spin conversion between the ortho and para species of the endohedral H 2 O was studied in the solid phase by lowtemperature nuclear magnetic resonance. The experimental data are consistent with a second-order kinetics, indicating a bimolecular spin conversion process. Numerical simulations suggest the simultaneous presence of a spin diffusion process allowing neighbouring ortho and para molecules to exchange their angular momenta. Cross-polarization experiments found no evidence that the spin conversion of the endohedral H 2 O molecules is catalysed by 13 C nuclei present in the cages.

Symmetry-breaking in the endofullerene H2O@C60 revealed in the quantum dynamics of ortho and para-water: a neutron scattering investigation

“…This growth indicates that the doublet predominately arises from transitions originating in the para-H 2 O nuclear spin isomer. A more detailed analysis of the INS peak intensities as a function of time provides deeper insight into the kinetics of spin-isomer conversion, 17 however these details will be the subject of a future publication.…”

“…Recently, a cryogenic NMR investigation enabled a detailed investigation of the slow conversion over a period of 2 or 3 days from ortho-H 2 O to para-H 2 O. 17 The nuclear spin conversion was found to follow second order kinetics, demonstrating the process is bimolecular in origin and indicating neighbouring ortho complexes may play a role in mediating the process. The first INS experiments on H 2 O@C 60 4 were conducted on relatively impure material, leading to broad line shapes that masked important details in the spectrum.…”

Collisional cross-section of water molecules in vapour studied by means of 1H relaxation in NMR

“…In supercritical water171819, spin-rotation significantly contributes to NMR relaxation despite the high density. In the context of our attempts to prepare para -water20212223242526 and related spin states in other molecules272829303132, we have measured longitudinal relaxation rates R 1  = 1/ T 1 of gaseous H 2 O and HDO at different temperatures and pressures. To the best of our knowledge, this is the first time that such observations are reported.…”

The dipolar endofullerene HF@C60

“…[2][3][4] Recently the approach has been extended to C 70 and C 59 N. [5][6][7] The confined molecules display quantization of their coupled translational and rotational degrees of freedom, and exhibit phenomena such as nuclear spin isomerism and orthopara conversion. [8][9][10][11][12] Recently it was shown that nuclear spin conversion of the encapsulated water molecules in H 2 O@C 60 leads to a change in the dielectric constant of the material. 13 One system of great interest is HF@C 60 , in which each fullerene cage contains a single hydrogen fluoride (HF) molecule.…”