Laboratory measurements of absorption coefficients for the 727 nm band of methane at 77 K and comparison with results derived from spectra of the Giant planets

Abstract

A high resolution absorption spectrum of the 727 nm band of methane at 77 K is obtained using the intracavity laser spectroscopy technique. Absorption coefficients are determined and are reported as averages over 1 cm −1 intervals throughout the region 13,470–14,025 cm −1. An intensity of 753 cm −1 km −1 am −1 is obtained for the entire band. Positions of the vibration-rotation lines in this band are determined to an accuracy of ±0.02 cm −1 and, for the stronger lines, absorption coefficients at the center of the absorption line are reported. The results are compared with previous room temperature measurements on methane, with the gas phase band intensity calculated from measurements on liquid methane, and with absorption coefficients derived from methane features observed in the albedo spectra of the Giant planets and Titan.