Collision Shift in Methane

In this paper, the investigations at the 6-5, 7-6 and 8-7 transition of resolved hyperfine structure of the F₂ ⁽²⁾ P(7)v₃ methane line with the use of a He-Ne laser with a telescopic intracavity light beam expander at a wavelength of 3.39 mum was performed. The light beam diameter in the absorbing methane cell was of about 24 cm. The absorbing cell 8.5 m in length was placed into a permalloy jacket to eliminate the influence of the magnetic field. A second similar telescopic laser all parameters of which were kept constant was used as a frequency reference. In this case, the error of frequency measurements did not exceed 1 Hz, which corresponds in relative units to 10^-4