Atomic and molecular resonance absorption occurs predominantly at which part of the electromagnetic spectrum? (Think of rotational and some vibrational transitions in matter.)

Introduction:
Different materials exhibit resonant absorption at specific electromagnetic frequencies corresponding to physical processes such as electronic transitions, molecular rotations, and vibrations. This question focuses on where atomic and molecular resonances commonly appear for rotational modes and some vibrational modes relevant to matter–radiation interaction.

Given Data / Assumptions:

• Matter exhibits quantized energy levels for rotation and vibration.
• Rotational transitions typically lie in the microwave region; certain vibrational overtones extend into millimeter-wave/infrared.
• Macroscopic conductors at audio/AM frequencies primarily exhibit conduction and polarization losses, not discrete quantum resonances.

Concept / Approach:

Rotational energy levels of many molecules (e.g., water vapor, oxygen) have spacings corresponding to microwave wavelengths. Thus, microwave radiation efficiently couples to these transitions, producing strong resonance absorption and dispersion. While electronic transitions dominate the visible/UV and fundamental vibrational transitions lie in the infrared, the signature molecular rotational spectra are characteristic of the microwave band.

Step-by-Step Solution:

Verification / Alternative check:

Atmospheric attenuation peaks near 22 GHz (water vapor) and 60 GHz (oxygen) are practical demonstrations of molecular resonance effects in the microwave/mm-wave region.

Why Other Options Are Wrong:

• Very low or AM broadcast frequencies: energies are too small for discrete rotational/vibrational transitions.
• Visible band only: primarily electronic transitions, not rotational spectra.

Common Pitfalls:

Assuming all resonances are optical. In RF planning, microwave molecular resonances drive link budgeting due to atmospheric absorption not present at LF/MF.

Final Answer:

at microwave frequencies