Microwave spectroscopy

Microwave spectroscopy studies how matter interacts with microwave radiation. It measures molecular rotational transitions and magnetic resonance to reveal molecular structure and physical properties.

Molecular rotation: The rotational motion of molecules, governed by their moments of inertia and angular momentum. Microwave absorption commonly drives transitions between quantized rotational states.
Molecular structure determination: The inference of molecular geometry and bonding from experimental measurements. Rotational constants constrain bond lengths and molecular shape with high precision.
Rotational constant: A spectroscopic constant that relates a molecule's moment of inertia to its rotational energy spacings. It sets the characteristic spacing of a molecule's rotational spectral lines.
Infrared spectroscopy: Spectroscopy that measures infrared absorption or emission, often associated with molecular vibrations. Infrared spectra emphasize vibrational transitions, unlike microwave rotational line patterns.
Rigid rotor: An idealized molecule whose atoms remain at fixed distances while it rotates. Its energy-level model predicts the basic rotational spectrum of a diatomic molecule.
Molecular beam: A directed stream of atoms or molecules traveling through a low-pressure environment. Beam spectroscopy isolates molecules and reduces collisions that broaden spectral lines.
Moment of inertia: A measure of how mass is distributed relative to an axis of rotation. Rotational transition frequencies encode moments of inertia and therefore molecular dimensions.
Raman spectroscopy: Spectroscopy that measures frequency shifts in light scattered by molecular excitations. Raman activity depends on polarizability changes rather than a permanent dipole.
Rotational spectroscopy: Spectroscopy that measures transitions between quantized rotational energy levels of molecules. Microwave spectroscopy is a principal experimental method for rotational spectroscopy.
Fourier-transform microwave spectroscopy: A pulsed microwave technique that derives a molecular spectrum from a time-domain free-induction decay. It provides high-resolution rotational spectra of transient and stable molecules.

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