Fig. 4. NMR spectra recorded on the γ-alumina sample. (a) {1H-}27Al CT-CP spectra recorded at sample temperatures of ∼78 K (top, purple) and ∼36 K (bottom, orange) using MAS frequencies of 21 kHz and 13 kHz, respectively. (b) 1H Hahn-echo spectra recorded at a sample temperature of ∼105 K and a MAS frequency of 10 kHz with (red) and without (blue) μw irradiation suitable for CE-DNP. (c) The same as for (b) at the same intensity scaling, but at a sample temperature of ∼36 K. The signals in (b) and (c) recorded in the absence of μw irradiation have been magnified by a factor of 32 for illustrative purposes. Asterisks denote spinning sideband signals.
