POSITIONS AND INTENSITIES IN THE VIBRATIONAL SYSTEM $3\nu_{2}/\nu_{2}+\nu_{4}$ OF ${^{14}}NH_{3}$ NEAR $4 \mu m$.

Abstract

We report experimental line positions and intensities of the $3\nu_{2}$ and $\nu_{2} + \nu_{4}$ bands of ${^{14}}NH_{3}$ obtained from $0.011 cm^{-1}$ apodized resolution spectra recorded with the Fourier transform spectrometer at Kitt Peak National Observatory. 1366 lines with $J^{\prime} \leq 13$ have been assigned from which 1213 line positions with $(J^{\prime} \leq 12)$ are fitted using an effective rotation-inversion Hamiltonian to achieve a rms of $0.0069 cm^{-1}$. 726 intensity measurements are modelled to 12 terms of dipole moment expansion to $\pm 6%$. The band strengths of $3\nu_{2} (s-a)$ at $2384.15 cm^{-1}$, of $3\nu_{2} (a-s)$ at $2895.52 cm^{-1}$, of $\nu_{2} + \nu_{4} (s-s)$ at $2540.53 cm^{-1}$, and of $\nu_{2} + \nu_{4} (a-a)$ at $2586.13 cm^{-1}$ are $0.61(3), 0.244(7), 0.186(3)$ and $0.174(25) cm^{-2} atm^{-1}$ respectively. A prediction of the line parameters has been generated for all lines with intensities greater than $0.1.10^{-6} cm^{-2} atm^{-1}$ at 296K and submitted to HITRAN data base. Beside the lines belonging to the $3\nu_{2}/\nu_{2} + \nu_{4}$ system a number of strong features appear in the spectra which could be assigned by a preliminary study to the hot bands $(\nu_{3} - \nu_{2}), (\nu_{1} - \nu_{2}), (4\nu_{2} - \nu_{2})$. Implications about the suitability of the Hamiltonian used is explored, given that the experimental accuracy is a factor of about 10 times better that has been achieved by the fit.