Molecular spectroscopy

Molecular spectroscopy studies how molecules absorb, emit, or scatter electromagnetic radiation. Spectral features reveal molecular energy levels, structure, and motion.

Rotational spectroscopy: Spectroscopy of transitions between quantized rotational energy levels in molecules. Microwave absorption commonly reveals molecular moments of inertia and bond lengths.
Infrared spectroscopy: A technique that measures infrared absorption or emission associated chiefly with molecular vibrations. It is widely used to identify functional groups and characterize chemical samples.
Quantum mechanics: The physical theory describing matter and energy at atomic and subatomic scales. Quantized molecular states make spectroscopy's discrete transitions possible.
Absorption spectroscopy: Spectroscopy that measures radiation removed from a beam as it passes through matter. It is one of the three principal radiation–molecule interactions encompassed here.
Vibrational spectroscopy: Spectroscopy of transitions between quantized vibrational states of molecules. Infrared absorption tracks bond vibrations and functional groups.
Nuclear magnetic resonance spectroscopy: A method that uses radiofrequency transitions of nuclei in a magnetic field to determine molecular environments. It provides detailed structural information through molecular nuclear resonances.
Electromagnetic radiation: Energy transmitted through space as coupled electric and magnetic fields, including light and radio waves. Its frequency and interaction with molecules determine which transitions spectroscopy can probe.
Emission spectroscopy: Spectroscopy that measures radiation released by matter as it changes to lower-energy states. It probes molecular relaxation rather than the loss of incident radiation.
Electronic spectroscopy: Spectroscopy of transitions between electronic energy levels in atoms or molecules. Ultraviolet and visible light can promote molecules between electronic states.
Mass spectrometry: An analytical technique that separates ions by mass-to-charge ratio and measures their abundances. It complements spectra by identifying molecular masses rather than radiation-driven transitions.

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