High resolution infrared spectra of the ν1-ν4 bands of BiH3, and ab initio calculations of the spectroscopic parameters

The infrared spectrum of short-lived BiH₃ has been studied by Fourier transform technique. The BiH stretching bands ν₁/ν₃ at 1733.2546/1734.4671 cm⁻¹ and the bending fundamentals ν₂/ν₄ at 726.6992/751.2385 cm⁻¹ have been measured with a resolution of 5.5 and 6.6 × 10⁻³ cm⁻¹, respectively. The spectra were analyzed using different reductions of the rovibrational Hamiltonian accounting for the numerous resonance interactions in particular within the strongly Coriolis-coupled bending dyad. About 1150 and 980 transitions belonging to the ν₁/ν₃ and ν₂/ν₄ bands were fitted with an rms deviation of 0.62 and 0.53 × 10⁻³ cm⁻¹, respectively. High-level ab initio calculations at the coupled cluster CCSD(T) level with an energy-consistent small-core pseudopotential and large basis sets were carried out to determine the equilibrium structure, the anharmonic force field, and the associated spectroscopic constants of BiH₃. The theoretical results are in good agreement with the available experimental data.