2 Answer any two questions in this section.

  Value of this section: 20 marks

1. Carbon and oxygen each have two common isotopes ( and ; and  ). However, the abundances of the heavier isotopes are quite low (1% or less) in natural samples. Give a thorough qualitative description of the gas-phase IR spectrum of carbon monoxide.
2. List and briefly explain the approximations inherent in the Hückel molecular orbital method. Which of these approximations do you think are reasonable and which would you expect to be poor?
3. Explain how the Born-Oppenheimer approximation can be used to simplify the quantum mechanical molecular problem.