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Thesis Title: Subtitle - NMR Spectroscopy Research Group

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16 Chapter 1. Introduction.<br />

Figure 1.11 Illustration of the task performed by the software Possum.<br />

The software package requires the Δχ-tensor parameters to perform a<br />

structure based automatic assignment of the <strong>NMR</strong> resonances.<br />

1.3.2 The Δχ-tensor determination problem<br />

The Δχ-tensor determination problem consists of obtaining the eight parameters<br />

characterizing the Δχ-tensor such that the discrepancy between the observed and calculated PCS is<br />

minimal. These comprise the determination of the paramagnetic center location, of the Δχ-tensor<br />

orientation, and of the axial and rhombic component. The last two parameters characterize the<br />

shape of PCS effects that ranges between two extremes as illustrated in Figure 1.12.<br />

Figure 1.12 Isosurface shapes calculated by equation (1.1). The positive isolevel is shown in blue,<br />

the negative is shown in red. Both isolevels have the same absolute value. (a) When the rhombic<br />

component is equal to zero, the isosurface is axially symmetric (dotted line). (b) Isosurface when

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