Artefacts earliest

The earliest experimental data are from Hietanen and Sillen [1968HIE/SIL] in 3 M NaCl. They tested a number of different chemical models, all of which describe the experimental data with very nearly the same accuracy. Many of the species proposed occur in small amounts in the test solutions, cf. Appendix A, and this review suggests that most of them are artefacts, i.e., parameters that just improve the fit of the experimental data. The stoichiometry of these species does not have an obvious relationship to the known coordination chemistry of Th(IV), e.g., there are no known stmctures containing tri- and penta-nuclear complexes. However, the complex ThjlOH) is a predominant complex in a large concentration range and the equilibrium constant is not strongly dependent on the selection of other species accordingly, this review considers the complex (2,2) as well estabhshed. 

Digitisation of data during a 2D experiment is subject to the same thermal noise arising from the probe head and preamplifier as in a ID experiment, and this contributes to the noise baseplane observed in the 2D spectrum. There also exists a particularly objectionable artefact associated with 2D experiments, referred to as noise (note the here refers to the evolution period and should not be confused with the relaxation time constant). This appears as bands of noise parallel to the/i axis where an NMR resonance exists, and it is sometimes this that limits the observation of peaks in the spectrum rather than the true thermal noise. Indeed, it appears that the very earliest work on 2D NMR was unpublished due to excessive ti noise present in the spectra. Generally speaking, this is caused by... 

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