High-resolution infrared and millimeterwave spectra of the v3 = 1 vibrational state of 14NF3 at 907 cm-1

Abstract The ν 3 ±1 perpendicular band of 14 NF 3 ( ν 0 =907.541  cm −1 ) has been studied with a resolution of 2.5 × 10 −3  cm −1 , and 3682 infrared (IR) transitions ( J max =55, K max =45) have been assigned. These transitions were complemented by 183 millimeterwave (MMW) rotational lines ( J max =25, K max =19) in the 150–550 GHz region (precision 50–100 kHz). The kl =+1 level reveals a strong A 1 / A 2 splitting due to the l (2,2) rotational interaction ( q =−4.05 × 10 −3  cm −1 ) while the kl =−2 and +4 levels exhibit small A 1 / A 2 splittings due to l (2,−4) and l (0,6) rotational interactions. All these splittings were observed by both experimental methods. Assuming the v 3 =1 vibrational state as isolated, a Hamiltonian model of interactions in the D reduction, with l (2,−1) rotational interaction ( r =−1.96 × 10 −4  cm −1 ) added, accounted for the observations. A set of 26 molecular constants reproduced the IR observations with σ IR =0.175 × 10 −3  cm −1 and the MMW data with σ MMW =134 kHz. The Q reduction was also performed and found of comparable quality while the QD reduction behaved poorly. This may be explained by a predicted Coriolis interaction between v 3 =1 and v 1 =1 ( A 1 , 1032.001 cm −1 ) which induces a slow convergence of the Hamiltonian in the QD reduction but has no major influence on the other reductions. The experimental equilibrium structure could be calculated as: r e (N–F)=1.3676 A and ∠(FNF)=101.84°.