Cp. Jaroniec et al., Recoupling of heteronuclear dipolar interactions with rotational-echo double-resonance at high magic-angle spinning frequencies, J MAGN RES, 146(1), 2000, pp. 132-139
Heteronuclear dipolar recoupling with rotational-echo double-resonance (RED
OR) is investigated in the rapid magic-angle spinning regime, where radiofr
equency irradiation occupies a significant fraction of the rotor period (10
-60%). We demonstrate, in two model C-13-N-15 Spin systems, [1-C-13,N-15] a
nd [2-C-13, N-15]glycine, that REDOR Delta S/S-0 curves acquired at high MA
S rates and relatively low recoupling fields are nearly identical to the De
lta S/S-0 curve expected for REDOR with ideal delta-function pulses. The on
ly noticeable effect of the finite pi pulse length on the recoupling is a m
inor scaling of the dipolar oscillation frequency. Experimental results are
explained using both numerical calculations and average Hamiltonian theory
, which is used to derive analytical expressions for evolution under REDOR
recoupling sequences with different pi pulse phasing schemes. For xy-4 and
extensions thereof, finite pulses scale only the dipolar oscillation freque
ncy by a well-defined factor. For other phasing schemes (e.g., xx-4 and x (
x) over bar-4) both the frequency and amplitude of the oscillation are expe
cted to change. (C) 2000 Academic Press.