Populations. The acquisition of quantitative Si NMR spectra is often challenging and time-consuming due to extremely long longitudinal relaxation constants (T1). Therefore, we recorded three Si spin echo NMR spectra with recycle delays of 30, 60 and 90 min to estimate the Si T1 and populations of SiSi3H, SiSi3Cl and SiSi3OH (Figure ). Plotting of the signal intensity as a function of the recycle delay suggest the SiSi3H and SiSi3X (X = OH/Cl) Si NMR signals exhibit T1 of ca. 55 and 30 min, respectively (Figure ). Integration of the 60 min recycle delay Si NMR spectra reveals that the SiSi3H and SiSi3X groups correspond to ca. 63 and 37 % of Si atoms, respectively. However, the 60 min recycle delay was not quantitative (i.e., < 5×T1). The SiSi3H and SiSi3X populations were corrected by divided the relative signal intensity by )1 -𝑒