THE POTENTIAL FUNCTION OF THE HCN BENDING MODE IN FULMINIC ACID, A QUASI-LINEAR MOLECULE

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1973

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Ohio State University

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Thirteen vibration-rotation transitions in the spectrum of HCNO and twelve in the spectrum of DCNO, all below $800 cm^{-1}$, have now been measured and assigned. The rotational analysis of the four lowest-lying transitions of HCNO provided the basis of the assignment. The completed assignment confirms our earlier suggestion that the potential function for $\nu_{5}$, the lower of the two degenerate bending modes, may be described by a two dimensional isotropic oscillator perturbed by a potential hump. The spectrum of DCNO establishes also that the perturbed mode is primarily an HCN (DCN) bend, in which very little contribution from the skeletal bending coordinate, the CNO bend, is present. Approximate methods have been used to determine parameters which describe the $\nu_{5}$ potential function. The parameters determined using different approximate Hamiltonians are not identical, but each set of parameters describes a low barrier opposing linearity, with the ground state lying approximately $60 cm^{-1}$ above the top of the barrier. The barrier height was determined to be about $100 cm^{-1}$. The fulminic acid spectrum thus presents the first opportunity to study the fully resolved rotational and rovibrational spectrum of a truly quasilinear molecule in the ground electronic state.

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This work was supported by a grant from the Deutsche Forschungs gemeinschaft.
Author Institution: Institut f\""ur Physikalische Chemie, Universit\""{a}t Kiel

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