Question

Why doesn’t molecular hydrogen produce an FTIR spectrum? Explain.

Answer 1

Explanation:

FTIR spectroscopy is method which is used to determine structures of the molecules with characteristic absorption of the infrared radiation by the molecule.  

When the molecules is exposed to the infrared radiation, the sample molecules absorb the radiation of wavelengths (specific to molecule) which causes change of the dipole moment of the sample molecules. The vibrational energy levels of the sample molecules consequently transfer from the ground state to the excited state.  

Frequency of absorption peak is determined by vibrational energy gap.

Intensity of absorption peaks is related to change of dipole moment and possibility of transition of the energy levels.  

Thus, by analyzing infrared spectrum,abundant structure information of the molecule can be known.  

Most of the molecules/ compounds are infrared active but for homo-nuclear molecules which are diatomic like $H_2$, $N_2$, $Cl_2$, $O_2$ are inactive due to zero dipole change in vibration and the rotation of such molecules.