First high–resolution analysis of the dyad of ²⁸SiD₄: Appearance of the isotopic substitution properties in the XY₄ (T_d-symmetry) molecules

The high resolution infrared spectra of SiD₄ were recorded with a Bruker IFS125 HR Fourier transform interferometer and analysed in the region of 550–800 cm−1 where the bands ν₄ and ν₂ are located. The 7279 transitions with J^max. = 37 were assigned to the ν₄/ν₂ dyad (the ν₂ band is forbidden in absorption for symmetry reasons, and its transitions can appear in the spectrum only because of Coriolis interaction with the allowed ν₄ band). The subsequent weighted fit of experimentally assigned transitions was made with the Hamiltonian model which takes the resonance interactions between the (0001) and (0100) vibrational states into account. The initial values of the Hamiltonian parameters have been predicted on the basis of the isotopic substitution theory. As the result, a set of 33 fitted parameters was obtained which reproduces the initial 7279 ro–vibrational transitions with the drms=1.85×10⁻⁴ cm−1 which corresponds to the experimental uncertainties.