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Homework Help: Best way to calculate UV-Vis absorption onset?

  1. May 21, 2016 #1
    1. The problem statement, all variables and given/known data
    I have a bunch of UV-Vis spectra to analyze and I am having a hard time choosing what the "onset" of each spectrum is, which I will use to calculate the optical band gap of each spectrum.

    2. Relevant equations

    3. The attempt at a solution
    I read somewhere that plotting wavelength vs. (wavelength*Absorbance)^2 and then fitting through the linear portion of the graph, where the intercept corresponds to the onset.
    By calculating the first derivative and checking the zero point after the last saddle point could also yield the onset? thanks
  2. jcsd
  3. May 22, 2016 #2
    Tauc plots are typically used.
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