Fourier transform infrared and millimeter-wave study of the v2=1, 2 and the v2=v4=1 rovibrational states of 14NF3

The 21 (A 1 ; 647.13cm - 1 ), 2 2 (A 1 ; 1292.26cm - 1 ) and 2 1 4 1 (E; 1138.28cm - 1 ) excited states of 1 4 NF 3 have been studied by high-resolution FTIR spectroscopy with a resolution between 2.3 and 3.0 x 10 - 3 cm - 1 ,and by millimeter-wave (MMW) spectroscopy. For the 2 1 state, 3380 non-zero weighted (NZW) υ 2 infrared (IR) transitions (J m a x =K m a x = 70) and 59 MMW transitions (J m a x = 27, K m a x = 21) were fitted together, with respective rms deviations σ I R = 0.142 x 10 - 3 cm - 1 and σ M M W = 28 kHz, using an unperturbed model up to sextic centrifugal distortion constants. The lower state parameters were constrained to those of the ground state. Similarly we have fitted 2181 NZW transitions (J m a x = K m a x = 60) of the 2υ 2 - υ 2 hot band merged with 54 MMW transitions (J m a x = 21, K m a x = 13) measured in the 2 2 state and employing the 2 1 parameters for the lower state. Respective rms deviations were σ I R = 0.263 x 10 - 3 cm - 1 and σ M M W = 58 kHz. The anharmonicity constant x 2 2 = -1.00606(1)cm - 1 was determined. The υ 2 = 2 state is better determined by the 2υ 2 - υ 2 rather than the obtained 2υ 2 IR data owing to the weakness of 2v 2 . To the contrary the strong and isolated υ 2 + υ γ 1 4 combination band is much better suited to probe the 2 1 4 1 state than the υ 2 + υ γ 1 4 - υ γ 1 4 hot band. Therefore 4375 NZW IR lines (J m a x =K m a x = 69) of v 2 + v 4 and 119 MMW transitions belonging to the 2 1 4 1 state with J m a x = K m a x = 13 were fitted together using the same model as for the v 4 fundamental band. This model takes into account l(2, 2), l(2,-1), l(2, -4), and (0, 6) intravibrational interactions when the D reduction of the Hamiltonian is employed. The corresponding rms of deviations were σ I R = 0.270 x 10 - 3 cm - 1 and σ M M W = 227 kHz; similar rms values were also obtained for Q and QD reductions refining uniformly 22 parameters. The anharmonicity constant x 2 4 = -2.27995(3) cm - 1 was determined.