11.5: Problems/Questions

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1. At what wavelength in nanometers would the Stokes and anti-Stokes Raman lines for carbon tetrachloride (218, 314, 459, 762, and 790 cm^-1) appear if the source was (a) a helium/neon laser at 632.8 nm, (b) solid state laser at 785 nm , and (c) a nitrogen laser at 337 nm.

2. Why does the ratio of anti-Stokes to Stokes intensities increase with sample temperature?

3. What is a virtual state?

4. Why is fluorescence such a problem in Raman Spectroscopy?

5. Of the three laser sources described in Problem 1, which will yield the strongest Raman signals (has the best scattering power) and which is most likely to give problems due to fluorescence ?

6. Suggest two or three ways in which one might distinguish whether an observed peak obtained on laser excitation is caused by fluorescence or Raman scattering.

7. For vibrational states, the Boltzmann equation can be written as N₁/N₀ = exp (-delta E/kt) where N₀ and N₁ are the populations of the lower and upper energy states, respectively. delta E is the energy difference between the states, k is the Boltzmann constant (1.38066 x 10^-23 J/K = 0.695035 cm^-1/K) and T is the temperature is Kelvins. For temperatures of 25 degree Celsius and 100 degree Celsius, calculate the ratio of the intensities of the Stokes and anti-Stokes lines for CCl₄ at (a) 218 cm^-1, (b) 459 cm^-1, and (c) 790 cm^-1.

8. Do a brief search of the web for notch filters for Raman spectroscopy and identify what is a notch filter and why are they useful in Raman instruments