Very low temperature spectroscopy: The pressure broadening coefficients for CH3F between 4.2 and 1.9 K

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Abstract
Pressure broadening parameters and cross sections for the CH3F–He system have been measured between 4.2 and 1.9 K by means of a recently developed technique based on collisional cooling in a cryogenic cell. The cross sections for the K=0 and K=1 components of the J=1–2 transition were found to be 75.2 and 66.6 Å2, respectively, at 4.2 K and 55.5 and 54.5 Å2, respectively, at 1.9 K. The cross sections at 4.2 K are about 50% larger than the 300 K values. These results are compared with earlier experimental and theoretical results obtained for the CO–He system.