High resolution infrared spectra and rovibrational analysis of the coupled ν2/ν5 bands of D3Si35Cl

The Fourier transform infrared spectrum of monoisotopic D3Si35Cl in the region of the ν2/ν5 band system was recorded with a resolution of 2.4 × 10−3 cm−1. More than 9000 lines of the strongly Coriolis x,y-coupled bands, (ν2)0 = 701.936, and (ν5)0 = 688.898 cm−1, have been assigned, among them 276 forbidden but perturbation allowed transitions around avoided crossings according to Δ(k−ℓ)=±3 mechanisms. Three different models taking into account redundancies in the framework of unitary equivalent reductions of the rovibrational Hamiltonian have been employed to fit the data. All three models reproduced consistently the full data set employing 28 refined parameters with an rms deviation of 0.31 × 10−3 cm−1. The equivalence of the parameter sets was established by the agreement of parameter sums obtained with the different models. The analysis of the avoided crossings, together with the fit of the forbidden lines, allowed an independent determination of the ground state parameters A0 and DK0. Combined with existing data for ν1, ν3, ν4, and ν6, the present results allowed the determination of experimental values, Ae = 1.4371895(94) and Be = 0.19823049(59) cm−1. The experimental results are compared with those of previous ab initio calculations of the anharmonic force field.