Diode laser spectroscopy of the ν6 band of methyl fluoride

The five Q branches, ^PQ₁, ^RQ₀, ^RQ₁, ^RQ₂, and ^RQ₃, of the ν₆ band of methyl fluoride ¹²CH₃F were observed by using a tunable diode laser spectrometer and were analyzed to obtain the following molecular constants (in cm^?1): $\text{ν}\text{?}{}_6\text{= 1182.67605(80)}$, A₆ = 5.2006(14), (Aζ)₆ = 1.5437(11), and (Aζ)₆η_K = 1.6(11) × 10^?4, with 2.5 times the standard errors in parentheses. The precision of the band origin may, however, be 0.001–0.002 cm^?1 because of the wavelength uncertainties of the N₂O spectral lines used as the references. An analysis of the ^RQ₀ subband determined the sign of the q₆ constant to be positive. The α₆^A, α₆^B, and q₆ constants of methyl fluoride are discussed in terms of the anharmonic potential field.