The scattering mean free path in the Uranian atmosphere

New measurements of the equivalent widths of the 4.0 S(0) and S(1) H2 quadrupole lines in the Uranian spectrum have been obtained using high dispersion (4.12 A/mm) image-tube spectrography. The measured equivalent widths are 62 plus or minus 19 mA and 58 plus or minus 13 mA for the S(0) and S(1) lines, respectively. Curve-of-growth analysis in terms of a reflecting layer model yields an H2 column density of 780 (+940 or -330) km amagat and a temperature of 78 (+80 or -24) K. Interpretation using a semiinfinite, homogeneous, isotropically scattering model for line formation yields a scattering mean free path at 6400 A of 550 plus or minus 250 km amagat. Quoted errors for both the H2 column density and the scattering mean free path include the effect of uncertainty in the choice of atmospheric temperature. The results are discussed in terms of current models for the Uranian atmosphere.