Spectra of coincidence of CH3F IR absorption with CO2-laser emission at pressures of 2, 10 and 60 Torr were recorded by the use of a photoacoustic detection method in the whole range of CO2-laser emission. The spectra show that CH3F absorbs many CO2-laser lines in the range 1084-1071 cm-1 with the strongest absorption at 1046.80 cm-1, laser line P(20). Absorption is predominantly due to the fundamental of nu-3, which is well spread over the whole laser emission range. The intensities of all absorptions rise with increasing pressure, but some absorptions change their relative intensity with respect to one another. In addition, the fine structure of the line spectrum, characteristic of lower pressure samples, disappears as pressure is increased.
