The spectroscopic analysis of the v₂=1, v₅=1, and v₃=v₆=1 infrared vibration system of H₃SiI

The ν2 (A1)/ν5 (E)/ν3+ν6 (E) band system of H3(28)SiI was investigated using Fourier transform infrared spectra recorded from 820 to 1100 cm(-1) at a resolution of 2.0×10(-3) cm(-1). In total, 11,903 transitions were assigned. Additional 1466 transitions reaching the v3=v6=1 state were obtained from the ν3+ν6-ν6 and ν3+ν6-ν3 hot bands near 360 and 590 cm(-1), respectively. Moreover, 30 highly accurate CO2 laser sideband transitions of the (r)Q0 branch of ν5 (J.M. Frye, W. Schupita, and G. Magerl, J. Mol. Spectrosc. 128, 427 (1988)) were implemented in the data set with J(max)″=140 and K(max)″=21. To adequately reproduce the complex pattern of interacting levels the Hamiltonian employed included 14 off-diagonal terms. These comprise x,y Coriolis ro-vibration resonances, between ν2/ν5, ν2/ν3+ν6 and ν5/ν3+ν6, and the anharmonic Fermi resonance between ν5/ν3+ν6. All these resonances strongly perturb the v2=1, v5=1, and v3=v6=1 excited states whose rounded deperturbed vibrational term values are 904.5, 941.1, and 953.7 cm(-1), respectively. In addition, the Δl=Δk=±2 l-resonance was found to be active within the v3=v6=1 state and between v5=1 and v3=v6=1; the Δl=±2,Δk=∓1 l-resonance within the v5=1 state and between v5=1 and v3=v6=1 was established, as well as the Δl=±1,Δk=∓2 α resonance between v2=1 and v5=1. A standard deviation of the fit, 0.48×10(-3) cm(-1), resulted which is ca. three times the estimated precision of experimental wavenumbers. Improved J-dependent ground state parameters of H3SiI were obtained by fitting 5420 combination differences, σ(fit)=0.22×10(-3) cm(-1).