gasesabsorb

Gasesabsorb describes the capacity of gaseous molecules to absorb electromagnetic radiation at specific wavelengths, producing absorption lines or bands. This phenomenon is fundamental to spectroscopy and atmospheric science, because it allows the identification and quantification of gases in a mixture or in the atmosphere.

Absorption arises from transitions between energy levels in the molecules. Electronic transitions dominate in the ultraviolet and visible, while vibrational-rotational transitions dominate in the infrared. The strength of absorption depends on the absorption cross section, the concentration (number density) of the gas, and the path length of light. For dense gases, line shapes are influenced by Doppler broadening, while pressure broadening from collisions further modifies widths.

Quantitative description uses the Beer-Lambert law: I = I0 exp(-σ(λ) N L), where I is transmitted intensity, σ(λ) is the spectral cross section, N is the number density, and L is the optical path length. Temperature and pressure affect population of energy levels and the widths of spectral lines, altering the observed absorption.

Applications include atmospheric science, where absorption by water vapor, carbon dioxide, methane, and ozone shapes the Earth's radiation budget; astronomy, where absorption lines reveal chemical composition of stars and interstellar gas; and industrial sensing, where spectroscopy monitors gas concentrations and pollution.