Chapter 11, Problem 11A.1DQ

Interpretation Introduction

Interpretation:

The physical origin of selection rule has to be stated.

Concept introduction:

The gross selection rule for pure rotational transition is that the molecule must possess a permanent electric dipole moment.  The molecules possessing dipole moment is considered as a handle that stirs the electromagnetic field into oscillation.  Polar molecules possess electric dipole moment and thus are classified as microwave active.