Figure 20. Accordion Spectroscopy.

(a) In an accordion experiment, the evolution time, t₁, and the mixing time, τ_m, are increased simultaneously. The expanding pulse sequence can be likened to the bellows of an accordion. (b) The sampling points in an accordion experiment trace out a radial spoke, but unlike most radial experiments, one of the two dimensions is a mixing time rather than a chemical shift. The proportionality constant relating the simultaneous increases in the two experimental parameters is κ, which determines the slope (and therefore the angle) of the radial spoke. (c) A schematic representation of the data that would result from the accordion experiment. The lineshapes of the diagonal and cross-peaks reflect the dynamics of the exchange process observed during the experiment. (d) The peaks in an accordion spectrum can be inverse-Fourier-transformed to reveal the buildup curves. Shown here are the transforms of one diagonal peak (top) and one crosspeak (bottom) from cis-decalin, measured at 240 K in a Bruker 300 MHz spectrometer. Panels (c) and (d) are reprinted from [82].