Fixed doublet ratio

Figure 1 Three line-position and line intensity roadmaps as a function of rotation angle (deg), for rotations about three orthogonal rotation axes, obtained from solid-state 31P cross-polarization (CP) NMR spectra at fixed magnetic fields of 4.7 T, for single-crystals (space group C2/m) of TMPS (tetramethyldiphosphine sulfide). One sees the spectra from two site types occurring in abundance ratio 1 2, each with a spin-spin doublet structure. Taken from Ref. 31.

The P2p signal is a doublet with 2pi/2 and 2p3/2 components their theoretical energy separation (0.9 eV) and the intensity ratio ofO.5 have been fixed for the curvefitting analyses of all P2p spectra. The binding energy of the P2ps/2 component was at 134.7 0.1 eV. The results of qualitative and quantitative analysis are. summarized in Table 1. 

Curve fitting may be carried out either in a "free manner or using constraints. Generally, the use of physically realistic contraints results in a fit that is more physically acceptable. Typical examples of the use of constraints would be the fixing of the Zpj/i to 2pi/2 ratio in an overlapping doublet from a simple element such as sulfur or phosphorus, at least initially, and to. set equal the linewidths of the two components. Alternatively, where different chemical forms of the same element are known to be present in certain ratios, that information could be included in the fit. For example, in the curve-fitted carbon l.v spectrum of the fluoropolymer hexafluoropropylene-vinylidene fluoride shown in Fig. 4, the areas of the three components of the hexatluoropylene block, namely CFj, CF2 and CF. are equal. The CF> and CH2 components of the vinylidene fluoride monomer are also of equal intensity, and a very satisfying fit is found. 

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