MISMATCHING CROSS-POLARIZATION IN THE ROTATING-FRAME

A Hartmann-Hahn type of cross-polarization experiment is performed with dipolar order in the rotating frame instead of Zeeman order as is the usual case. Under matched Hartmann-Hahn conditions, ω1S = ω1I, no polarization is transferred. Under mismatched conditions, however, a positive or a negative polarization is acquired depending on whether ω1S > ω1I or ω1S < ω1I and also on the sign of the initial spin temperature of the dipolar order. The polarized S signal has a maximum intensity when the mismatch amount |ω1S - ω1I| has the same order of magnitude as the local field produced by the homonuclear and heteronuclear dipolar interactions. This behavior can be described qualitatively by a spin-temperature hypothesis. © 1993 by Academic Press, Inc.