Centralizer theory for long-lived spin states

Abstract

Nuclear long-lived spin states represent spin density operator configurations that are exceptionally well protected against spin relaxation phenomena. Their long-lived character is exploited in a variety of Nuclear Magnetic Resonance (NMR) techniques. Despite growing importance of long-lived spin states in modern NMR strategies for their identification have changed little over the last decade. The standard approach heavily relies on a chain of group theoretical arguments. In this paper we present a more streamlined method for the calculation of such configurations. Instead of focusing on the symmetry properties of the relaxation superoperator, we focus on its corresponding relaxation algebra. This enables us to analyse long-lived spin states with Lie algebraic methods rather than group theoretical arguments. We show that the centralizer of the relaxation algebra forms a basis for the set of long-lived spin states. The characterisation of the centralizer on the other hand does not rely on any special symmetry arguments and its calculation is straightforward. We outline a basic algorithm and illustrate advantages by considering long-lived spin states for some spin-1/2 pairs and rapidly rotating methyl groups.

Nuclear singlet relaxation by chemical exchange

“…The relaxation mechanisms of LLS have been extensively studied 3,6,15,[60][61][62][63][64][65][66][67][68][69][70][71] .…”