HEED extended pulse sequences

The application of HEED extended pulse sequences has opened the way to the measurement of isotope shifts A / NCX) in natural abundance of N (0.37 %). 

Previously it was necessary to use N labelled samples in order to determine isotope shifts A N(X). By the application HEED extended pulse sequences,it proved possible to determine these parameters for numerous compounds in the natural abundance of (0.37%). Table 11 lists a number of these data and an example for the application of the HEED INEPT pulse sequence is shown in Fig. 9. 

The application of HEED extended pulse sequences makes it possible to determine 1A14/15N(207Pb) values at natural abundance of the nuclei,86107 and it is hoped that by application of this technique a larger set of these data for lead-nitrogen compounds will become available in the future. 

Any HETCOR pulse sequence can readily be extended by a Hahn-echo pulse train [20] which is particularly useful in the case of Sn/ H HEED-HETCOR of tin-nitrogen compounds. This enables one to measure y( Sn, N), /( N, H) (together with the relative signs) and A / N( Sn), all at the same time (see Figure 13). Numerous other modifications of 2D HETCOR experiments are feasible, many of which are based on schemes of selective excitation and/or... 

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