Question

Please help me answer the following questions:

(iv) Calculate the molar extinction coefficient (molar absorptivity) of the maximum absorbance of the spectrum in Figure 1.

(v) Estimate the wavenumber gap between the vibrational levels that gives the vibronic structure apparent in the spectrum of anthracene. Check your answer before proceeding to answer the next question. (Note: the peaks are a single vibronic progression so you can average your estimates of the wavenumber gap.)

5 M compound (2) Figure 1: Absorbance spectrum of anthracene (5 UM) in water in a 1 cm path length cuvette. Absorbance (A) -0.02 LULUU 300 320 340 420 440 360 380 400 Wavelength / nm

Answer 1

Explaination :-

Absorbance (optical Density) Molar extinction coefficient (molar absorptivity) is constant for a given compound at a specific wavelength and concentration. Mathematically, A = Ech e = T A CL where, A= absorbance ca concentration L = path length in moes/L (cm) Here, from given figure absorbance & 0.08. concentration & SuM -- - 5x10' M. length of cuvette = 1cm path is E400 0.08 5x100 x 1 0.016 X106 16000 L mol am 1 =

Explaination and solution

How is band wave number gop gap / vibronic related to band ggel absorbancez a a from n absorbance spectroscopy, when sample is irradiated it absorbs photon in its orbit. Transition lover energy to higher enegg place absorbing at a particular and equal to Eg. conduction band AE = Eg=ho he t valence brand, We can value putting of cakulate Eg by & in Eg = ha o - 1.98x10 2 J.m. 400 x 10m 400 nm Teq = 1.98 x 10-15 Important t Note: However actual calculated using which we plot vibronic Tanc (Eho - gay can be Equation for A (ho-E).

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