Rotational analysis of the inversion–vibration spectrum of ¹⁵NH₂D: A set of interacting states ν₅/ν₆/2ν₂

High–resolution (0.004 cm−1) Fourier transform spectra of the ¹⁵NH₂D molecule were recorded for the first time in the region of 1000–1800 cm−1 at LISA in Créteil and analyzed. Assignments of transitions were made on the basis of the Ground State Combination Differences method. Parameters of the effective Hamiltonian of the ground vibrational state in the model of the asymmetric top molecule in A−reduction and I^r−representation were determined from the fit of MW and FIR data known in the literature. As a result of the analysis, about 4380 ro-vibrational transitions have been assigned to the five vibrational states (v₅=1,s),(v₅=1,a),(v₆=1,s),(v₆=1,a), and (v₂=2,s), and the values of 647 upper ro-vibrational energy levels were determined. A weighted fit was carried out using the model of the effective Hamiltonian which takes into account strong resonance interaction between all five upper vibrational states corresponding to the observed (v₅=1,s),(v₅=1,a), (v₆=1,s), (v₆=1,a), and (v₂=2,s), and interaction of these five states with an unobserved sixth state (v₂=2,a). A set of 168 parameters obtained from the fit provided the basis to reproduce the initial 647 energy values (line positions of about 4380 transitions) of the five mentioned inversion–vibrational states with the drms=7.9×10⁻⁴ cm−1.