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Atomic spectroscopy studies the emission, absorption and scattering associated with the energy levels of chemical atoms and ions. The positions of spectral lines identify differences of energy, while their strengths and polarization also depend on populations and selection rules.

A dilute-gas discharge can excite chemical atoms; a spectrometer then separates the emitted light by wavelength. Comparing the resulting lines with an independently calibrated reference can identify an element or reveal an isotope shift. Changing a magnetic field tests Zeeman splitting, and improving energy resolution can reveal fine structure. Different experimental changes therefore isolate different pieces of the atomic model.

An inductively coupled plasma receives power through electromagnetic induction. An alternating coil electric current produces a changing magnetic field, which induces an electric field in the gas. Electrons accelerated by that field transfer energy through collisions, sustaining ionization and driving atomic transitions.

A typical analytical source surrounds a gas-carrying dielectric torch with a radiofrequency coil. Excited atoms emit spectral lines useful for atomic spectroscopy, while extracted ions can feed mass spectrometry. The coil supplies energy without requiring it to touch the plasma. Coupling, gas composition and particle losses determine the discharge response. ^[ref]

Spectroscopy investigates how a system emits, absorbs or scatters signals as a function of frequency, wavelength or energy. A spectrum can identify transition energies, response strengths and line shapes. In atomic spectroscopy, a photon connects two energy levels through $h\nu =|E_f-E_i|$; in inelastic scattering, both energy and momentum transfers can matter.

A simple optical experiment passes source light through a sample, disperses the transmitted light and compares it with a reference. An absorption line identifies reduced transmission over a spectral interval, but its depth also depends on the sample amount and instrumental response. Wavelength calibration and energy resolution distinguish an intrinsic feature from a shifted or broadened recording. The inference therefore uses a response model as well as a list of line positions.

An atomic physicist who coauthored a NIST compendium of atomic spectroscopy with Wolfgang Wiese. It connects the labeling of energy levels with spectral lines, transition strengths and selection rules. These conventions allow a measured spectrum to be compared with tabulated atomic data without confusing a level designation, a wavelength and an intensity.^[ref]

An atomic physicist who coauthored a NIST reference on atomic spectroscopy with William C. Martin. Its treatment of transition probabilities distinguishes the probability of an atomic transition from the population of its initial energy level. This matters because the strength of an observed spectral line depends on both atomic properties and the conditions of the emitting sample.^[ref]