New Aspects of Spin Diffusion and Cross Relaxation in Solid-State NMR

Area of Science:

• Solid-state Nuclear Magnetic Resonance (NMR) spectroscopy
• Spin dynamics and relaxation mechanisms
• Molecular dynamics in crystalline solids

Background:

• Spin diffusion is a crucial mechanism influencing magnetic relaxation in solids.
• Understanding motional effects on spin diffusion is key to interpreting NMR data.
• Spin diffusion of quadrupolar order and its relation to cross-relaxation require further investigation.

Purpose of the Study:

• To compare and validate theoretical models of motionally driven spin diffusion.
• To experimentally investigate spin diffusion in deuterated biphenyl driven by molecular flips.
• To elucidate the relationship between spin diffusion of quadrupolar order and cross-relaxation.

Main Methods:

• Application and comparison of theoretical models for spin diffusion.
• Experimental verification using Nuclear Magnetic Resonance (NMR) on single crystals of deuterated biphenyl and partially deuterated durene.
• Analysis of temperature-dependent spin diffusion and cross-relaxation processes.

Main Results:

• Theoretical predictions for spin diffusion (S = 1/2 and S = 1) were quantitatively confirmed by experiments.
• Molecular flip processes in deuterated biphenyl were identified as the drivers of temperature-dependent spin diffusion.
• Spin diffusion of quadrupolar order was observed to degenerate into cross-relaxation in partially deuterated durene.

Conclusions:

• Motional processes significantly influence spin diffusion, with molecular flips providing a clear experimental example.
• Cross-relaxation is a key process in solids, explaining why quadrupolar order relaxation times (T 1Q) are often shorter than spin-lattice relaxation times (T 1).
• The study provides a comprehensive understanding of spin diffusion and cross-relaxation in molecular solids.