High resolution study of the lowest inversion–vibration bands of 15NHD2: Interacting bands ν5/ν6/2ν2

Abstract 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 Creteil 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 and 70 new mean combinations differences obtained in the present study. As the result of the analysis, 4168 ro-vibrational transitions have been assigned to the five vibrational states ( v 5 = 1 , s ) , ( v 5 = 1 , a ) , ( v 6 = 1 , s ) , ( v 6 = 1 , a ) , and ( v 2 = 2 , s ) , and the values of 667 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 ( v 5 = 1 , s ) , ( v 5 = 1 , a ) , ( v 6 = 1 , s ) , ( v 6 = 1 , a ) , and ( v 2 = 2 , s ) . A set of 102 parameters obtained from the fit provided the basis to reproduce the initial 667 energy values of the five mentioned inversion–vibration states with the drms = 4.26 × 10 − 4 cm − 1 .