DETERMINATION OF INTEGRATED-INTENSITIES OF OVERLAPPED IR BANDS BY CURVE-FITTING, FOURIER SELF-DECONVOLUTION AND A COMBINATION OF BOTH METHODS

Curve-fitting, Fourier self-deconvolution, and a combination of these methods have been applied to determine integrated intensities of the b ands arising from the C=O stretching mode of n-octanoic acid. When the se bands are separated by more than an average band width, the mc,st r eliable results are supplied by curve-fitting. However, simple functio ns (Gauss or Lorentz) do not satisfactorily describe shapes of experim ental bands, and more complex profiles should be used such as the sum or product of the Gauss and Lorentz functions or their convolution (Vo igt profile). The applied Fourier self-deconvolution procedure assumes Lorentzian band shapes; therefore the determined intensities of the b ands that deviate from this profile are always higher than the true va lues. An analysis combining the two methods mentioned above did not im prove the results. The output bands from curve-fitting, with a high Lo rentzian fraction, might have overestimated the band areas. Thus, the integration should be done over a limited wavenumber range. Our result s clearly show that the band-shape function plays an important role du ring the determination of the integrated intensities using curve-fitti ng, Fourier self-deconvolution or a combination of both methods (refer red to in this paper as the ''combined method'').