Which of the following options correctly describes the effect of infrared (IR) radiation on a molecule?

• A. It excites electrons to higher energy orbitals.
• B. It induces nuclear spin transitions.
• C. It causes the molecule to undergo vibrational transitions.
• D. It breaks chemical bonds within the molecule.

Answer: (C)

Verified step by step guidance

1. Understand the nature of infrared (IR) radiation: IR radiation has energies that correspond to the vibrational energy levels of molecules, not electronic or nuclear energy levels.
2. Recall that electronic transitions require higher energy photons, typically in the ultraviolet or visible range, so IR radiation does not excite electrons to higher orbitals.
3. Recognize that nuclear spin transitions are associated with radiofrequency radiation, as seen in NMR spectroscopy, not IR radiation.
4. Know that IR radiation causes molecules to absorb energy that leads to changes in their vibrational states, meaning the bonds within the molecule vibrate more intensely but do not break.
5. Conclude that the correct effect of IR radiation on a molecule is to cause vibrational transitions, which is the basis for IR spectroscopy used to identify functional groups in molecules.