Counting spins with a new spin echo double resonance

Area of Science:

• Nuclear Magnetic Resonance Spectroscopy
• Solid-State Chemistry
• Quantum Spin Dynamics

Background:

• Traditional spin echo double resonance (SEDOR) relies on echo amplitude dependence on pulse spacing (tau).
• This method involves flipping observed spins (S) and refocusing pulses on observed spins (I).
• Limitations exist in analyzing spin-spin coupling with conventional SEDOR.

Purpose of the Study:

• To introduce a novel SEDOR technique for quantifying spin-spin coupling.
• To determine the number of coupled spins (n) by measuring echo amplitude as a function of spin flip angle (theta).
• To provide a simpler and more powerful analysis, especially under strong collision conditions.

Main Methods:

• Measuring echo amplitude (M) as a function of the S spin flip angle (theta) at a constant pulse spacing (tau).
• Applying the method to amorphous silicon samples with 1H and 2D spins.
• Utilizing a magic angle spinning (MAS) version for multiply labeled alanine and urea.

Main Results:

• The variation of M with theta was successfully fitted to determine the number of coupled spins (n).
• Experimental data from amorphous silicon and labeled biomolecules confirmed the method's efficacy.
• Fourier transformation of M(theta) yielded a stick spectrum, with the highest stick indicating n.

Conclusions:

• The new SEDOR method provides a robust and straightforward way to determine spin-spin coupling numbers (n).
• This technique offers an alternative to multiple-quantum spin-counting methods.
• The findings are applicable to solid-state NMR and materials characterization.