Knowledge Bank

The interaction-induced absorption by collisional pairs of H$2$ molecules is an important opacity source in the atmospheres of the outer planets and cool stars . The emission spectra of cool white dwarf stars differ significantly in the infrared from the expected blackbody spectra of their cores, which is largely due to absorption by collisional H$2$--H$2$, H$2$--He, and H$2$--H complexes in the stellar atmospheres. Using quantum-chemical methods we compute the atmospheric absorption from hundreds to thousands of kelvin. Laboratory measurements of interaction-induced absorption spectra by H$2$ pairs exist only at room temperature and below. We show that our results reproduce these measurements closely, so that our computational data permit reliable modeling of stellar atmosphere opacities even for the higher temperatures.