Preparing initial conditions for rotational resonance in solid state NMR spectroscopy

✍ Scribed by Helen Geen; Malcolm H. Levitt; Geoffrey Bodenhausen

• Publisher: Elsevier Science
• Year: 1992
• Tongue: English
• Weight: 603 KB
• Volume: 200
• Category: Article
• ISSN: 0009-2614
• DOI: 10.1016/0009-2614(92)87002-7

✦ Synopsis

The internuclear distance between two homonuclear dipolar-coupled dilute spins-l/2, S* and Sx, can be measured by mtatianal resonance experiments in solid state NMR. These involve rotating the sample at the magic angle while fulfilling the condition for rotational resonance, f&-Q,= ncu,, where Q, and Q, are the isotropic shifts. Interpretation of the results is simplest if the spin system is prepared in a state of pure difference polarization, described by an initial density operator a( 1=0) =d=S$ -S:, regardless of the orientation of the crystallites. Preparation of such a state is a nontrivial task ifthe chemical shift anisotropy o.@uhx of one (or both) of the sites is comparable to the difference in isotropic shifts Q,,-Q, and hence to the required spinning speed w,= (&-fix) /n. It is shown how the difference polarization state d can be prepared by combining total sideband suppression (TOSS) sequences with their time-reversed counterparts, or by more condensed sequences of rotorsynchronized A pulses.