Second-order Coriolis resonance between ν 2 and ν 5 of CH 3F by microwave spectroscopy

The J = 1 ← 0 and J = 2 ← 1 transitions and the l-doubling transitions of J = 2 - 6 of ¹²CH ₃F in the ν₂ and ν₅ states were analyzed by taking into account the Coriolis interaction between the two modes. The molecular constants which are derived are: ν₅ - ν₂, 252 412 ± 112; B ₅^∗, 25 611.60 ± 0.40; A_ζ5 , -38 772 ± 116; B ₂^∗, 25 432.52 ± 0.33; D, 21 838.4 ± 8.2; q ₅^∗, 39.58 ± 0.30 MHz; in addition to a few other minor constants. The present result is completely consistent with the recent Raman data of Escribano, Mills, and Brodersen, J. Mol. Spectrosc.61, 249 (1976). Molecular constants in the ν₃ and ν₆ states have also been obtained: B₃, 25 197.570 ± 0.020; B₆, 25 418.917 ± 0.047; A_{ζ6 ηJ}, -0.562 ± 0.030; | q₆|, 8.70 ± 0.13 MHz. Errors are 2.5 times the standard deviations.