(a) (i) Which of the following four vibrations shown in Figure 2.1 will be Infrared active, and which will be Raman active? Provide brief explanations for your selection. [8 marks] (ii) Why is the number of vibrations shown for this molecule fewer than the number of vibrations that may be calculated by the 3N-6 rule? [4 marks] Ta + 1 3 + Y tetrahedral Vi symm stretch v bend V3 stretch v4 bend Figure 2.1. Normal modes of vibrations of tetrahedral XY4 molecule; arrows indicate directions of the corresponding atoms for these vibrations. (b) How would you remove chromatic aberration in Raman spectroscopy and FTIR spectroscopic imaging in transmission? Describe the approaches briefly and provide a couple of examples of applications where these approaches are beneficial. Support your explanation with corresponding schematics or figures as appropriate. [13 marks] (c) The Covid-19 global pandemic has resulted in alcohol-based hand sanitizers being used to wash hands, often from wall-mounted dispensers with the source and type of contents unknown to the user. The active ingredient in sanitizers is ethanol at the minimum concentration of 70% v/v. Which spectroscopic technique would you use to ensure that this threshold of ethanol is present in a dispenser? Explain which mode of the measurement you would use, which spectral bands and which calibration would you perform. Explain the advantage and limitation of your methodology. Support your explanations with corresponding schematics/figures. [13 marks]