Fig. 3.
Processing scheme for diagonal unfolding. (A) The original spectrum, processed in the standard manner, in which the diagonal signal (dashed line) is repeatedly folded in the F1 dimension. Spectra have been recorded with the pulse scheme of Fig. 2 A. The data matrix consists of 6*(t1) × 1,024*(t2) data points, with acquisition times of 144 ms (t1) and 307 ms (t2) (2T = 164 ms). Linear prediction was used to double the number of time-domain points in the F1 dimension, and both dimensions were apodized by cosine-squared functions and zero-filled by a factor of two before Fourier transformation. (B)An F1-dependent frequency shift is applied to the F2 dimension, such that the diagonal signals are now positioned vertically. (C) Vertical bands from the shifted spectrum are transposed and reassembled horizontally to construct an unfolded spectrum in the F1 dimension. (D) A 20-Hz band, corresponding to the center of the F2 dimension in C, is extracted, apodized by a sine-bell function, and then projected onto the F1 dimension, to yield a homonuclear decoupled 1D spectrum. The spectral widths for the horizontal and vertical dimensions are, respectively, 600 and 34.9 Hz. For display purposes, the vertical axis is expanded 2-fold relative to the horizontal axis.