Overtone spectrum of SiH stretching in H 2 SiCl 2

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The overtone spectra of H2SiCl2 molecule in the regions of 2000–9000cm −1 and 12000–12900cm −1 at room temperatures have been studied by use of high-resolution Fourier transform spectroscopy and sensitive-intracavity-laser absorption spectroscopy, respectively. The variations of vibrational quantum numbers Δ VSiH =1, 2, 3, 4 and 6 for the overtones of the SiH stretching have been analysed and assigned with the local mode model and the normal mode model. The values of harmonic frequency ωm , anharmonicity constant χm , bond coupling constant λ, the Morse oscillator parameters D e , α and interaction force constant f rr' are derived from the experimental spectrum with nonlinear least-squares fitting. The most striking feature of the SiH2Cl2 is that the larger the vibrational energy, the smaller the energy difference between a couple of lowest stretching states of a given manifold and finally, the couple of lowest stretching states are degenerated within the experimental error for Δ VSiH≥4 vibrational manifolds. The degenerate energy level structure resembles that of a diatomic Morse oscillator; the transition energies show a remarkable fit to the Birge–Sponer relation. The high vibrational states can be described straightforward with a SiH diatomic Morse oscillator wavefunction, this is an indication of vibrational bond localization.