Peak, asymmetrical width

Plotting diagrams showing dependence of peak parameters (such as peakedness, tailing, semi-half-width of peak, peak asymmetric etc.) on peak height ... 

If the peak is not symmetrical, different values will be calculated for n because the width measurements will not follow the predicted Gaussian distribution. In general, for asymmetrical peaks, n increases the higher up on the peak the width is measured. 

The assumption for the measurement of peak widths in Eqs. (8)—(10) is that the peak is Gaussian. Unfortunately, few peaks are truly Gaussian and, in general, for asymmetrical peaks, N, calculated by a Gaussian-based equation, increases the higher up on the peak the width is measured. Figure 3 shows the error in plate-count determinations for asymmetrical peaks as a function of the peak height at which the width is measured. A more accurate approach to efficiency measurement has been presented by Foley and Dorsey (7), which takes into account the peak asymmetry. 

It can also be noticed in Fig. 1 that spectral features for these three peaks are not symmetrical that is, their spectral shape deviates considerably from a simple Lorentzian line shape. Since the rotational contribution in the peak width in the PHOFEX spectrum is -1 cm-1, which is significantly smaller than the observed peak width, these asymmetrical spectral features are regarded as Fano-type profiles, which can appear in a spectrum for quasibound states. 

The half-width of all the absorption bands is approximately 1.5 e.v. When plotted on an energy scale the spectra are seen to be asymmetric on the high-energy side. If the asymmetric portion is deleted, the remaining symmetrically drawn peak has a half-width of about 1 e.v. for all five alcohols. 

The perpendicular drop should only be used if (1) the peaks are symmetrical and about the same height and width, (2) the valley between the peaks is no more than 5% of the peak height, (3) the baseline is flat, and (4) noise does not obscure the accurate placement of the baseline. If the peaks are asymmetrical, a perpendicular drop will overestimate the area of the smaller peak. Under those circumstances, a tangential skim may be a better approach. 

Table 7.4 summarizes the out-of-plane and in-plane epitaxial relationships of ZnO films and sapphire substrates, the c-axis and a-axis lattice constants of ZnO, the ZnO full peak widths at half maximum (FWHM) of 20-to and uj scans, and the tilt of the ZnO structure along surface normal [47]. Because of the low intensity of the asymmetric (10l4) reflection, the a-lattice constant has larger uncertainty compared to the c-axis lattice constant. The epitaxial relationships correspond to the results of Ohtomo (see Table 1 in [22]). 

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