Study of the ν₃ and 2ν₃ ← ν₃ bands of ¹²CH₃F by infrared laser sideband and submillimeter-wave spectroscopy

An infrared laser sideband spectrometer operating in the CO₂ laser region with 8- to 18-GHz sidebands has been used to record 266 transitions in the ν₃ band and 84 transitions in the 2ν₃ ← ν₃ band of ¹²CH₃F. The accuracy of the measured frequencies is estimated to be 1-3 MHz. A millimeter/submillimeter-wave spectrometer has been used to record the spectra of 48 pure rotational transitions in the ground vibrational state and 55 transitions in the v₃ = 1 vibrational state with an accuracy of 20-90 kHz. The new measurements have been combined with previous radio frequency and infrared laser results to derive sets of constants for the ground, v₃ = 1, and v₃ = 2 states for this molecule. Tables of the vibrational dependence of the parameters and of the near coincidences of the ν₃ and 2ν₃ ← ν₃ band transitions with CO₂ laser frequencies are given.