Multiple quantum NMR dynamics of spin-; carrying moleculesof a gas in nanopores

摘要

We consider the multiple quantum (MQ) NMR dynamics of a gas of spin carrying molecules innanocavities. MQ NMR dynamics is determined by the residual dipole-dipole interactions, whichare not averaged completely due to the molecular diffusion in nanopores. Since the averagednonsecular Hamiltonian describing MQ NMR dynamics depends on only one coupling constant, thisHamiltonian commutes with the square of the total spin angular momentum P. We use the basis ofcommon eigenstates of P and the projection of I on the external magnetic field for investigation ofMQ NMR dynamics. This approach allows us to study MQ NMR dynamics in systems consistingof several hundreds of spins. The analytical approximation of the stationary profile of MQcoherences is obtained. The analytical expressions for MQ NMR coherence intensities of thefive-spin system in a nanopore are found. Numerical investigations allow us to find thedependencies of intensities of MQ coherences on their orders (the profiles of MQ coherences) insystems consisting of 600 spins and even more. It is shown that the stationary MQ coherence profilein the considered system is an exponential one.