Chapter 1. Overview of Solid-State NMR
15
VNMR 6.1C User Guide: Solid-State NMR
01-999162-00 C0402
1.2 Spin-Lattice Relaxation Time
An additional characteristic of some nuclei in the solid state, for example
13
C, is a long
spin-lattice relaxation time (T
1
). To overcome this problem, the abundant nuclei (usually
protons) in the system are used. These are polarized with a spin locking pulse (CP). The
polarization is then transferred to the rare spins by applying an rf field at the Larmor
frequency of the rare spins that is of such a magnitude as to make the energy levels of the
abundant and rare spins the same in the rotating frame (Hartmann-Hahn match condition).
Following a transfer of energy from the polarized abundant spins to the rare spins, the rare
spin field is turned off and the resulting signal observed under conditions of high-power
proton decoupling. The recycle time is then set according to the proton T
1
, which is usually
much shorter than the rare spin T
1
.
The polarization transfer can give an increase in sensitivity. The rare spin response is
enhanced by a factor of up to the ratio of the magnetogyric ratios of the two spin systems.
For the
13
C-{
1
H} system, this is a factor of 4. However, as the enhancement is distance
related, caution should be exercised in using the cross-polarization experiment for
quantitative analysis.
1.3 Solids Modules, Probes, and Accessories
Varian supplies a complete line of solid-state NMR modules, probes, and accessories.
Solids modules include CP/MAS, wideline, CRAMPS/multipulse, and complete solids.
CP/MAS, wideline, and CRAMPS/Multipulse hardware and operation are covered in
Chapters 2, 3, and 4, respectively, of this manual.
The Varian complete solids module is capable of performing all experiments possible with
the Varian CP/MAS, wideline, and CRAMPS/multipulse modules. The major components
of complete solids module are the following:
For operation of the complete solids module, refer to the operations sections in the chapters
2 to 4 for the CP/MAS, wideline, and CRAMPS/multipulse modules.
A wide variety of solids probes and probe accessories are available, including wideline,
multipulse, and magic-angle probes.
Optional solids accessories include rotor synchronization, rotor speed controller, and the
solids variable temperature accessory. Chapter 5 covers using these accessories.
UNITY
INOVA
or UNITYplus System
Wideband ADC with Sum to Memory
Solids cabinet
High-band & low-band 1-kW amplifier
Pneumatics/tachometer box
MERCURYplus and MERCURY-Vx
systems
100 Watt High-band and 300 Low-band
amplifiers for CP/MAS experiments
Pneumatics/tachometer box
UNITY or VXR-S System
Wideband ADC
Solids cabinet
High-band & low-band 1-kW amplifier
Pneumatics/tachometer box
Wideband receiver
Sync module
Two fine attenuators