E.B. Mkadmi

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.

Analysis of FTIR spectra of CH2 79Br35Cl; the ν3 and ν9 fundamentals

The infrared spectrum of isotopically pure CH2 79BrCl has been recorded at a resolution of 0.0025 cm−1 and 0.0023 cm−1 (FWHM) in the range 600–1600 cm−1 with a Bruker IFS 120 HR Fourier transform spectrometer in Wuppertal. Here we report the full rotational analysis of the ν3 and ν9 fundamentals of the most abundant species CH2 79Br35Cl . Improved ground state constants, up to quartic terms, have been obtained from ground state combination differences (GSCD) involving transitions of the fundamentals ν3, ν4, ν5 and ν9. Both ν3 and ν9 transitions were fitted to a Watson-type Hamiltonian in the S-reduction, yielding accurate molecular constants for the ν3 and ν9 excited states. Small local perturbations were observed in both bands. Prominent features in the spectra were assigned to the ν3 and ν9 fundamentals of the CH2 79Br37Cl isotopic species and the hot-bands ν3+ν6 − ν6 and ν9+ν6 − ν6 of CH2 79Br35Cl.