Describe the behavior of water molecules from the interaction with electromagne – [Free] B99
Describe the behavior of water molecules from the interaction with electromagnetic radiation in the UV, IR, microwave, and radio regions. Choose the best option below.
Question:
Describe the behavior of water molecules from the interaction with electromagnetic radiation in the UV, IR, Microwave, and Radio regions. Choose between Bond Breaking, Nothing, Molecular Vibration, or Molecular Rotation.
Answer:
🔷 Ultraviolet (UV) Region
- UV photons have high energies (typically several electronvolts).
- Water molecules absorb UV radiation causing electronic excitation to higher energy states.
- At very high UV energy, photodissociation (bond breaking) can occur.
- Conclusion: UV radiation causes electronic excitation and possibly bond breaking.
🔶 Infrared (IR) Region
- Photon energies in this region match the energy needed for vibrational modes.
- Water molecules exhibit several vibrations: symmetric stretch, antisymmetric stretch, and bending modes.
- IR radiation is strongly absorbed by water due to efficient coupling to these vibrations.
- This explains IR absorption by atmospheric water vapor.
- Conclusion: IR radiation causes molecular vibration.
🔸 Microwave Region
- Microwave photons have lower energy (10⁻⁵ to 10⁻³ eV).
- Water is polar and has a permanent dipole moment.
- Microwaves excite rotational levels in water molecules.
- Reorientation of dipoles leads to energy dissipation as heat (basis of microwave ovens).
- Conclusion: Microwave radiation causes molecular rotation.
🔻 Radio Region
- Radio waves have the lowest photon energies.
- Insufficient to cause electronic, vibrational, or even lowest rotational transitions.
- Water has negligible absorption in this region.
- Radio interaction is mostly ignored unless using specialized techniques like NMR.
- Conclusion: Radio radiation results in nothing significant.
✅ Summary:
- UV Region: Electronic excitation and potential bond breaking.
- IR Region: Molecular vibration (strong absorption).
- Microwave Region: Molecular rotation (dipole interaction).
- Radio Region: No significant interaction.