Rotation spectrum and infrared fundamental bands of ¹²³SbD₃. Determination of molecular geometry and ab initio calculations of spectroscopic parameters

Abstract

The high resolution infrared spectrum of ¹²³SbD₃ has been recorded in the 20–350 cm⁻¹ range and in the regions of the ν₁, ν₃ and ν₂, ν₄ fundamental bands centred at 1350 and 600 cm⁻¹, respectively. Splitting 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 by means of a simultaneous fit of the rotational transitions and about 12 000 ground state combination differences from the infrared bands. The A and B reductions of the rotational Hamiltonian provided almost equivalent results. The molecular parameters of the ν _i  = 1 (i = 1 − 4) states were obtained as a result of 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 rovibrational interactions of Coriolis and k-type that have been treated explicitly in the model adopted for the analysis. Improved effective ground state and equilibrium geometries were determined for the molecule and compared to those of ¹²³SbH₃. Ab initio calculations at the coupled cluster CCSD(T) level with an energy-consistent large-core pseudopotential and large basis sets were carried out to determine the equilibrium structure, the anharmonic force field, and the associated spectroscopic constants of ¹²³SbH₃ and ¹²³SbD₃. The theoretical results are in good agreement with the experimental data.

Acknowledgements

This work was carried out within the frame of the SPHERS network (HPRN-CT-2000-00022). We thank the EC for financial support. E.C., G.D.L., and L.F. acknowledge the financial support of the Università di Bologna and of the Ministero dell’Istruzione, dell’Università e della Ricerca.

Notes

Note that in our previous work [28] the calculated Coriolis coupling constants ζ₁₃ ^y and ζ₂₄ ^y in AsH₃, ¹²¹SbH₃, ¹²³SbH₃, and BiH₃ were erroneously assigned to be positive. Using the correct negative sign for these constants, the predicted sense of the intensity perturbations [28] is reversed and is then in agreement with the present study.