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Discussion Questions
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4.5 Discussion Questions
- Explain how colour can arise from molecules.
- Electronic transitions for molecules occur in the UV-vis regime.
One limitation of UV-vis spectroscopy for molecules is the lack of specificity. Discuss what this means and why this is so.
Despite its limitation(s), UV-vis spectroscopy is widely used in research labs. What are some common uses of UV-vis spectroscopy?
- The figure below is a simulated rotation spectrum of CO. Estimate the internuclei distance of CO.
- The molecule Cyanoacetylene \text{HC}_{3}\text{N} exhibits a spectral line at 9.098 GHz for the J=1\rightarrow0 transition.
What is the rotational constant in units of GHz?
In what catagory of the EM spectrum does this line belong to? (radio/microwave/IR/visible/UV/X-ray)
What are the positions of the spectral lines corresponding to the transitions J=2\rightarrow1, J=3\rightarrow2, J=4\rightarrow3, etc.?
Simulate the rotational (emission) spectrum of Cyanoacetylene \text{HC}_{3}\text{N} at T=10 K, 50 K and 100 K.
- Derive an expression for the most probable J transition line for rotational spectroscopy. (Hint: use Eq.(QM(6))).
Suggest how we can estimate the temperature of the observed object using rotational spectroscopy.
- By referring to the following figure, suggest why the range of isotopes would result in a different wavenumber.
