Question

Which of the following events may occur when IR radiation is absorbed?

Relative nuclear spins of nucleii with non-zero Io's are changed.

Bonding electrons are promoted to higher energy molecular orbitals.

More intense IR absorptions occur for those bonds having greater dipole moment changes with bond lengthening in a vibration.

Vibrational amplitudes of bonds are increased.

Intra-molecular bond angles are changed.

Answer 1

IR RADIATION IS MORE ENERGETIC THAN MICROWAVES AND RADIOWAVES SO ALL THE PHENOMENON WHICH OCCUR IN THESE CASES OCCUR WHEN AN IR ABSORPTION OCCURS.

HENCE

Relative nuclear spins of nucleii with non-zero Io's are changed.

More intense IR absorptions occur for those bonds having greater dipole moment changes with bond lengthening in a vibration.

Vibrational amplitudes of bonds are increased.

Intra-molecular bond angles are changed.

BUT Bonding electrons are promoted to higher energy molecular orbitals CANNOT OCCUR BECAUSE PROMOTION OF BONDING ELECTRONS REQUIRES UV OR VISIBLE LIGHT HENCE IR RADIATION DOES NOT HAVE SUFFICIENT ENERGY TO CARRY OUT THIS HENCE THE ELECTRONIC TRANSITION DOES NOT TAKE PLACE.