JOURNAL OF MAGNETIC RESONANCE 35.373-377 (1979) Absorption Spectra From Phase-Modulated Spin Echoes

A method is presented by which pure absorption spectra can be derived from spin echoes with a symmetric envelope amplitude, but with arbitrary phases 4 in the centers of the echoes. It is shown that without any phase correction, absorption spectra can be obtained in which the amplitudes of the spectral lines are either proportional to cos 4 or sin (b. or independent of q%. As an example a T2 measurement of 1,1,2-trichloroethane is given. In many NMR techniques, for instance in the DEFT (1) and SEFI (2) experi-ments, in T2 measurements, and in most kinds of 2D J spectroscopy (3), one is confronted with the fact that the phases of the signals at the center of the echo are modulated because of the spin-spin coupling in the molecule (4,5). In many cases of one-dimensional spectroscopy one can eliminate this phase disturbance only by making an absolute-value calculation (5); this introduces line broadening. In most kinds of 2D J spectroscopy the phase modulation is used as the spreading parameter in the second time dimension (3,6, 7). After 2D Fourier transformation, lineshapes are obtained with a so-called “phase-twist ” (6). From this it is impossible to obtai