Absorption coefficients for the CH4 6190-Å band as a function of temperature from 290 to 100°K are reported. We have developed and used a laser intracavity photoacoustic spectroscopy method which permits accurate control of the sample temperature due to the small sample volume required. Over the temperature interval from 290 to 100°K, we found the peak absorption coefficient to increase from 0.6 to 1.0 cm-1 (km-am)-1. The peak absorption increase was accompanied by significant band shape changes. The low-temperature data were then used to constrain further the Baines and Bergstralh (1986, Icarus 65, 406-441) standard model atmosphere for Uranus and found to yield an excellent fit to the bandshape near the minimum of the 6190-Å band. The new low-temperature coefficients reduce the pressure level needed to fit the Neff et al. (1984, Icarus 60, 221-235) photometric data, as well as the Voyager Uranus observations, to ∼3 bar, rather than the 7-10 bar required by the room temperature CH4 absorption coefficients, thus producing agreement between models derived from individual H2 quadrupole lines and CH4 lines. The limitations of the present data are discussed in the context of the observations. © 1990.
