Which of the Following Molecule is not IR Active?

Answer - Molecules such as H2, N2, and O2 are not IR active.

The bands are IR active (Raman inactive) for asymmetric vibrations and symmetric vibrations to highly symmetric polyatomic molecules with a centre of inversion (IR inactive). Raman can be dormant while an IR mode is active, and vice versa, but not simultaneously.

Some vibrations are passive to infrared. For instance, the stretching vibrations of totally symmetrical double and triple bonds do not alter the dipole moment, and as a result, do not cause any light to be absorbed (but other bonds and vibrational modes in these molecules do absorb IR light). Molecules such as H2, N2, and O2 are not IR active.

Summary:

Which of the Following Molecule is not IR Active?

Molecules such as H2, N2, and O2 are not IR active. H2, N2, and O2 are examples of homonuclear diatomic compounds that have no dipole moment and are inactive in the IR.