The ν1 and ν3 band system of 15NH3

The infrared spectrum of (NH3)-N-15 has been investigated by high-resolution Fourier transform infrared spectroscopy in the region of the stretching fundamentals. A large number of ro-vibration transitions in the 3050-3650 cm(-1) spectral range has been recorded and assigned to the fundamentals nu(1) and nu(3), and to the 2 nu(4) overtone bands. In total, 1606 transitions involving the (s) and (a) inversion-rotation-vibration levels have been identified and assigned. They include 256 perturbation-allowed transitions with selection rules Delta K = +/- 2, Delta l = -1 in nu(3) and Delta l = +2 in 2 nu(+/- 2)(4), and Delta K = +/- 3, Delta l = 0 in nu(1) and 2 nu(0)(4). All assigned transitions were fitted simultaneously to a model Hamiltonian that includes all symmetry-allowed interactions between and within the excited state levels in order to obtain accurate sets of spectroscopic parameters for both inversion states. The standard deviation of the fit, 0.034 cm(-1), is about 70 times larger than the estimated measurement precision. This result is similar to that reported for the same band system in (NH3)-N-14 by Kleiner et al. [J. Mol. Spectrosc. 193, 46 (1999)] and is a consequence of the neglect of vibration and ro-vibration interactions between the analysed states and vibrationally excited states with close energies.