The ν 1 and ν 3 band system of 15NH3

The infrared spectrum of 15NH3 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 cm1 spectral range has been recorded and assigned to the fundamentals 1 and 3, and to the 24 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 DK¼2, Dl¼1 in 3 and Dl¼þ2 in 22 4 , and DK¼3, Dl¼0 in 1 and 204 . 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 cm1, is about 70 times larger than the estimated measurement precision. This result is similar to that reported for the same band system in 14NH3 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.