Multiple quantum NMR dynamics of spin-1/2 carrying molecules of a gas in nanopores

TL;DR

This paper investigates the dynamics of multiple quantum NMR in gas molecules within nanopores, revealing that the stationary MQ coherence profile is exponential and providing analytical and numerical insights into large spin systems.

Contribution

It introduces an analytical approach for studying MQ NMR dynamics in large spin systems in nanopores, accounting for residual dipole interactions and diffusion effects.

Findings

Stationary MQ coherence profile is exponential.

Analytical expressions for five-spin MQ coherence intensities.

Numerical results for systems with over 600 spins.

Abstract

We consider the multiple quantum (MQ) NMR dynamics of a gas of spin carrying molecules in nanocavities. MQ NMR dynamics is determined by the residual dipole-dipole interactions which are not averaged completely due to the molecular diffusion in nanopores. Since the averaged non-secular Hamiltonian describing MQ NMR dynamics depends on only one coupling constant, this Hamiltonian commutes with the square of the total spin angular momentum $\hat I^2$. We use the basis of common eigenstates of $\hat I^2$ and the projection of $I$ on the external magnetic field for investigation of MQ NMR dynamics. This approach allows us to study MQ NMR dynamics in systems consisting of several hundreds of spins. The analytical approximation of the stationary profile of MQ coherences is obtained. The analytical expressions for MQ NMR coherence intensities of the five-spin system in a nanopore are found. Numerical investigations allow us to find the dependencies of intensities of MQ coherences on their orders (the profiles of MQ coherences) in systems consisting of 600 spins and even more. It is shown that the stationary MQ coherence profile in the considered system is an exponential one.