Emission Spectra. Electrons move rapidly around the nucleus in energy shells. If their energy is increased, then they can jump to a higher energy level. The process is reversible, so electrons can return to their original energy levels. When this happens, they emit energy.

Developing a quantitative atomic absorption method requires several considerations, including choosing a method of atomization, selecting the wavelength and slit width, preparing the sample for analysis, minimizing spectral and chemical interferences, and selecting a method of standardization.

Emission and absorption spectra form the basis of spectroscopy, which uses spectra to provide information about the structure and the composition of a substance or an object. In particular, astronomers use emission and absorption spectra to determine the composition of stars and interstellar matter.

The result is an absorbance spectrum that shows the intensity of emission as a function of wavelength. As is the case for emission spectra, absorbance spectra range from narrow lines to broad bands. The atomic absorption spectrum for Na is shown in Figure \(\PageIndex{4}\), and is typical of that found for most atoms.

A material's absorption spectrum is the fraction of incident radiation absorbed by the material over a range of frequencies of electromagnetic radiation. The absorption spectrum is primarily determined [2] [3] [4] by the atomic and molecular composition of the material.