THEORETICAL STUDY OF PRESSURE BROADENING OF POTASSIUM RESONANCE LINES BY HELIUM ATOMS

Abstract

Pressure broadened line profiles of alkali-metal atoms are prominent in the spectra of brown dwarfs and may be a source of opacity in extrasolar giant planet atmospheres. Accurate calculations of these profiles are important in developing effective diagnostics of the temperatures, densities, albedos and composition of the atmospheres of these objects. Quantum mechanical calculations are performed of the absorption profiles of the potassium (4s-4p) resonance line under the influence of a helium perturbing gas. We use carefully constructed potential energy curves and transition dipole moments to compute the absorption coefficients at temperatures from 500 to 3000 K at wavelengths between 400 nm and 800 nm. Contributions from quasi-bound states are included. The resulting red and blue wing profiles agree well with previous theoretical calculations and with experimental measurements.