Question

Q 3(a) [5.33 Marks]
Indicate which of the following molecules you expect will show microwave (rotational)
spectra; O2, CH4, O3, N2, CHCl3 and CS2. In each case, briefly explain your
answers.

Q 3(b) [18 Marks]
The microwave spectrum of ¹²C¹⁶O shows a series of lines spaced 3.824 cm-1
apart.

Assuming a rigid rotor:
(i) Calculate the moment of inertia for this molecule.
(ii) Estimate the C-O bond length.
(iii) Determine which rotational level (J) is most populated at 300 K.

Q 3(c) [10 Marks]
Using a rotational energy level diagram for a rigid rotor draw an energy level diagram
showing the first four energy levels for 12CO and 13CO. Using relevant equations,
discuss the impact of isotopic substitution on the rotational spectrum of CO.

Answer 1