Rotation spectrum and high resolution infrared spectra of the fundamental bands of 121SbD3. Determination of the ground state and equilibrium structures. Ab initio calculations of the spectroscopic parameters

The high resolution infrared spectrum of 121SbD3, recorded between 20 and 350 cm−1 and in the regions of bending and stretching fundamental bands, centred at 600 and 1350 cm−1, has been analysed. Splittings of the K″=3, 6 lines have been observed both in the rotation and ro-vibration spectra. A large number of 'perturbation allowed' transitions with selection rules Δ(k−ℓ)=±3, ±6 and ±9 have been identified in all fundamental bands. Accurate ground state molecular parameters have been determined fitting simultaneously the rotational transitions and about 9000 ground state combination differences obtained from lines assigned in the ro-vibrational spectra. The A and B reductions of the rotational Hamiltonian have been applied in the analysis of the ground state. They provided almost equivalent results. The molecular parameters of the 11, 21, 31 and 41 states have been obtained from the simultaneous analysis of the ν1 (A1)/ν3 (E) stretching and of the ν2 (A1)/ν4 (E) bending dyads. In fact, the corresponding excited states are affected by strong perturbations due to Coriolis and k-type rovibrational interactions that have been treated explicitly in the model adopted for the analysis. Improved effective ground state and equilibrium geometries have been determined and compared to those of 121SbH3 and of 123SbD3. Ab initio calculations at the coupled cluster CCSD(T) level with an energy-consistent large-core pseudopotential and large basis sets have been carried out to determine the equilibrium structure, the anharmonic force field, and the associated spectroscopic constants of 121-stibine. The theoretical constants and structural parameters are in good agreement with the experimental data.