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Generalized Voigt


Voigt Generalization Convolution Models

PFChrom offers two different models for testing the integrity of Voigt model fits to spectroscopic data:

Gaussian Student's t (Area)

This is an convolution model used to check the validity of Voigt model fits.

a0 = Area

a1 = Center

a2 = Gaussian Width

a3 = Lorentzian Width

a4 = Student's t nu (1=Lorentzian, Infinite=Gaussian)

 

Built in model: Gauss<S>

User-defined peaks and view functions: Gauss[S]i[amp](x,a0,a1,a2,a3) (Warning: computed as integral, very slow!)

 

This is a symmetric convolution of a Gaussian and a Student's t which can be used to fit Voigt peaks where the Lorentzian component is estimated with a Student's t that will be a Lorentzian only with the a4 nu=1. If the tails of the non-Gaussian component of the convolution are not perfectly Lorentzian, this model will fit to a value other an a3=1. A Lorentzian has wide tails which may be subject to instrumental sampling, digitization, and filtering. The Lorentzian component of a pure Voigt should fit very close to a4=1.0 if there is a significant Lorentzian component to the Voigt. The peaks below vary from a4=1 to a4=1.5.

v5_Spectroscopy_Gauss[S]i.png

Lorentzian Student's t (Area)

 

a0 = Area

a1 = Center

a2 = Lorentzian Width

a3 = Gaussian Width

a4 = Student's t nu (1=Lorentzian, Infinite=Gaussian)

 

Built in model:Lorentz<S>

User-defined peaks and view functions: Lorentz[S]i(x,a0,a1,a2,a3) (Warning: computed as integral, very slow!)

 

This is a symmetric convolution of a Lorentzian and a Student's t which can be used to fit Voigt data where the Gaussian component is estimated with a Student's t that is a Gaussian only with nu at infinity (PFChrom's upper bound on nu is 1,000,000). If the tails are not perfectly Gaussian, this model will fit to a value with a nu lower than this maximum. This model can be used to test the integrity of the Gaussian component of a Voigt peak. If any portion of that which contributes to the Gaussian line spread function has wider tails, this will be strongly reflected in a4. If a pure Voigt is fit, you should expect values of a4 10,000 or higher, if there is a significant Gaussian component to the Voigt. The peaks below vary from a4=5 to a4=1,000,000.

v5_Spectroscopy_Lorentz[S]i.png



c:\1pf\v5 help\home.gif Voigt Pearson VII