Temperature dependence of ν3 and ν4 bandwidths and complex refractive indices for crystalline methane

Abstract

Infrared spectra of thin films of pure CH4 have been measured for a range of temperatures from 22 to 68 K. The bandwidth for the fundamental ν3 near 3000 cm−1 (3.3 μm) varies from 12.7 to 33.2 cm−1, while that for ν4 near 1300 cm−1 (7.7 μm) varies from 6.2 to 16.0 cm−1. The real and imaginary parts of the index of refraction also exhibit significant dependence on temperature. These broadband measurements at low temperatures are useful for an understanding of clouds and hazes in the atmosphere of Uranus, clouds and ices in the atmosphere of Titan, and ices on the surfaces of Pluto and Triton.