Analysis of the v₃ and v₁ infra-red bands of SiH₄

Abstract

The high-resolution infra-red spectrum of SiH₄ in the region 2101 cm^-1 to 2265 cm^-1 has been analysed. Most of the lines observed have been assigned to transitions of the v ₃ and v ₁ bands of the abundant isotopic species ²⁸SiH₄. The v ₁ band is formally forbidden in the infra-red, but a vibration-rotation interaction between v ₁ and v ₃ lends intensity to the v ₁ transitions. The spectrum has been fitted by diagonalizing the v ₃ = 1 and v ₁ = 1 hamiltonians coupled by the vibration-rotation interaction term. 500 transitions have been fitted with an overall standard deviation of 0·007 cm^-1, using only 15 adjustable parameters (ten in the v ₃ = 1 hamiltonian, four in the v ₁ = 1 hamiltonian, and one interaction coefficient). The calculated intensities are also in good agreement with experiment. Transitions of the other isotopic species ²⁹SiH₄ and ³⁰SiH₄ have also been observed, but these spectra have not been analysed in detail.