The V4 = 1 state of 14NF3 at 493 cm-1 studied by high-resolution FTIR, centimeter-wave, and millimeter-wave spectroscopy

Abstract The ν 4 band of NF 3 , ν 0 =493.423 cm −1 , has been studied by FTIR spectroscopy with a resolution of 3×10 −3 cm −1 . Strong intensity perturbation by l (2, 2) resonance is revealed. The more than 5000 IR assignments were complemented by 132 millimeter-wave measurements in the regions 140–250 and 340–470 GHz, by 7 new or formerly reported J =1–0 and 3–2 microwave frequencies, and by 134 Δ J =0, Δ k =Δ l =±2 direct l -type centimeter-wave transitions in the region 8–26 GHz with J max =22 and ( k − l ) max =15. The rotational data enabled detection of splittings caused by l (2, −4) ( t ) and (0, 6) ( h 3 ) interactions in excess to those by l (2, 2) ( q ) effects. The A 1 A 2 splitting of the k l =−2 level was not detected on the Δ K =−1 IR transitions owing to their vanishing intensity for J >18. In contrast, A 1 A 2 doublets were observed in transitions with 28≤ J ≤43 reaching the k l =+4 level. All appropriately weighted observations were fitted together to 28 free parameters up to sextic terms employing three different ( D , Q , QD ) reductions of the rovibrational Hamiltonian, and the equivalence of the reductions was established. The sets of molecular constants obtained from the merged data reproduce the IR observations with σ=0.24×10 −3 cm −1 , the millimeter-wave data with σ=29 kHz, and the centimeter-wave measurements with σ=3 kHz.