Improved Ground State Constants for Molecular Hydrogen

The quality of spectra recovered from planetary sources continue to improve. High resolution spectroscopic instruments from space craft as well as orbiting and ground based telescopes are capable of both high spatial and spectral resolution allowing detailed characterization of individual spectral lines. Improved atmospheric modeling and the retrieval of pressure and temperature profiles can be achieved by having accurate laboratory information on line positions, pressure broadening, line shapes and density shifts of key molecular spectra. This paper reports the determination of the density shift coefficient for the 3-0 S(1) line of H₂ using a tuneable diode laser and the Denison 22 meter White-type cell configured for 4 km of optical path. Densities to 3 amagats were used to determine this parameter. Density shift coefficients are now available for most of the 35 quadrupole lines measured for molecular hydrogen and have been used to compute the zero-density positions of these spectral lines. A new set of molecular constants for the ground rotational-vibrational states of H₂ have been determined using these data. This work has been supported in part by NASA Grant NAG5-4341 and by Denison University.