Optical constants of solid hydrocarbon films produced in a glow discharge

Optical constants of films produced in a glow discharge have been found. The films produced in the discharge contained methane, hydrogen and helium. The hydrocarbon chains formed in the plasma chamber are also present in the atmospheres of Uranus and Neptune. The films have two distinct regions; a light central region and a dark outer region. The density and the real and imaginary part of the refractive index are consistantly higher in the outer regions of the films. The outer region most likely has a higher carbon content which causes the higher density and optical constants. The optical constants for both regions have similar slopes. In the visible region the n values decrease as the wavelength increases and then remain relativly constant in the infrared region.

The k values also decrease with increasing wavelength in the visible region reaching a minimum between 1.2μm and 2.5μm. The k values then rise in the infrared region and show absorption peaks. These peaks were identified with absorption peaks of known hydrocarbon chains.