[en] Theory and experiment are being used together to explore spectra from sodium and xenon gas mixtures similar to those used in high pressure lamps. Results from high precision measurements of the absorption coefficients over the wavelength range from 425 to 760 nm are presented with 0.02 nm spectral resolution. Measurements of the sodium density with ±5 percent uncertainty complement the absorption coefficient measurements. The experimental data are compared to quantum-mechanical spectral calculations that utilize recent cold collision and other data. The spectra are sensitive to the interatomic potentials, especially in the far wings in which molecular features such as vibrational-rotational and satellite structures are exhibited. The particular results for Na-Xe are analyzed in detail