The v₂ = 1, 2 and v₄ = 1 bending states of ¹⁵NH₃ and their analysis at experimental accuracy

¹⁵NH₃ is the object of extensive investigation due to the central role of ammonia in astronomical sciences and to the complexity of modeling its interacting vibrationally excited states. Of major interest in astrochemistry is the determination of the ¹⁴N/¹⁵N ratio in space, characterized by unexpected variability among different solar system objects and reservoirs. Recently, the spectroscopic analysis of ground and v₂ = 1 a, s states of ¹⁵NH₃ has been completed at experimental accuracy. Here, the characterization of the a, s inversion symmetry levels of v₂ = 1, 2 and v₄ = 1 states is presented. New spectra of ¹⁵NH₃ have been recorded from 325 to 2000 cm^-1 at a resolution ranging from 0.00096 cm^-1 to 0.003 cm^-1, using the Canadian Light Source synchrotron at CLS. 7518 transitions covering nine bands, ν₂, 2ν₂, ν₄, 2ν₂ ← ν₂, ν₄ ← ν₂, 2ν₂ ↔ ν₄ and the inversion-rotation transitions in the excited states, have been fitted simultaneously. The effective Hamiltonian adopted includes all symmetry allowed interactions between and within the studied excited states, according to the most recent results on ammonia. The transitions have been reproduced at experimental accuracy using 185 spectroscopic parameters, determined with high precision. The leading diagonal parameters, G_v, B, C, D's, compare well with those of ¹⁴NH₃. The wavenumbers of the assigned transitions are compared with their theoretically predicted values. An improved set of ground state parameters is also derived. These results noticeably improve the wavenumber line list in the high-resolution transmission molecular absorption (HITRAN) database.