The direct l-type resonance spectrum of CF3CCH in the vibrational state ν10 = 2

The direct l-type resonance spectrum of CF3CCH in the vibrational state ν10 = 2 has been measured by means of waveguide microwave Fourier transform spectroscopy in the range 8-26 GHz. Two types of direct l-type resonance transitions induced by the (Δk = ±2, Δl = ±2) interaction could be observed: 262 transitions following the ΔJ = 0, Δk = Δl = 2 selection rule covering values of J = 17-64 and G = ∣k − l∣ from 2 to 15, and 75 transitions following the ΔJ = 0, Δk = Δl = 4 selection rule covering values of J = 44-70 and G up to 3. The strong (2, 2) resonance furthermore allowed the observation of A1-A2 splittings of the k = l = ±2 states from J = 63-70. The transitions with G = 3 showed splittings due to the (4, −2) and (0, 6) interactions. The corresponding energy level systems and part of the Hamiltonian matrix are discussed. Strong perturbations due to Δ(k − l) = 3 interactions coupling the states k = ±1, l = ±2 and k = ±4, l = ±2 made possible the observation of perturbation-allowed transitions with selection rule k = ±1, l =± 2 ↔ k = 0, l = ±2. Additionally, the J = 2-1 and 3-2 rotational transitions have been measured. A multiple fitting analysis has been performed in which the experimental data have been fitted using five reduced forms of the effective Hamiltonian as proposed by Sarka and Harder [J. Mol. Spectrosc. 197 (1999) 254]. Parameters up to sixth order have been determined including the axial rotational constant A for both values of ∣l∣ and the unitary equivalence of the determined parameter sets has been demonstrated.