Comparison of theoretical and experimental red and near infrared absorption spectra in overheated potassium vapour

The K2 molecular spectra have been theoretically and experimentally investigated in the wavelength range between 550 nm and 1100 nm and at the temperatures between 650 K and 1100 K. Semiclassical theoretical simulations were performed using the most recent data for the potential energy curves for the K(4S)+K(4S) and K(4S)+K(4P) systems and the relevant dipole transition moments. The measurements of the corresponding spectra were performed by a spatially resolved absorption method in an inhomogeneous overheated potassium vapour generated in a heat pipe. Both theoretical and experimental investigations confirmed that the reduced absorption coefficients of the potassium diffuse triplet bands at 575 nm, 721.5 nm and 1095 nm are practically independent of temperature in a wide temperature range. The obtained data for the reduced absorption coefficients of these bands can be used for a simple and accurate determination of potassium atom number densities in the range from 5×1016 cm-3 to 5× 1018 cm-3.