Question

c) What is the criterion for a molecule to be
rotationally active ?​

Answer 1

Answer:

Gross Selection Rule: molecules with permanent dipoles are microwave active (the molecule must be polar), e.g. heteronuclear diatomics - HCl, CO, NO, etc. Homonuclear diatomics are microwave inactive (e.g. O2, N2, etc.) In other words, a dipole must be present in the molecule for you to get a rotational spectrum.