Pressure broadening coefficients for an infrared transition of the methyl radical have been measured for the first time. CH 3 radicals, generated by pyrolyzing di-tert-butyl peroxide in a flow of either N 2 or Ar, were probed using a tunable diode laser and a multipass absorption cell. The Lorentz half-width of theQ(6,6) line of the ν 2 band of CH 3 at 607.024 cm −1 was measured as a function of pressure at 295 K. The broadening coefficients (HWHM) areb(Ar) = 0.0310 ± 0.0012 cm −1 atm −1 andb(N 2 ) = 0.0390 ± 0.0020 cm −1 atm −1 . These coefficients are lower than those for CH 4 –Ar, N 2 broadening. This may be due to a lower polarizability or smaller effective hard collision diameter for CH 3 relative to CH 4 .