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    The Fermi doublet, v1 and 2v2, of ClCN at high resolution
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    The vibration-rotation structure of the infrared absorption bands due to ν21+ν3, 2ν20+ν3, and ν1+ν3 have been observed and measured for Br79CN and Br81CN. The average value of α3 for these two isotopic molecules was found to be +0.000677 cm—1. The Fermi resonance constant for the resonance diad was calculated to be W12=35.41 cm—1 for Br79CN and W12=35.48 cm—1 for Br81CN. The positions of the Q branches of a number of other bands were also measured.
    Diad
    Fermi resonance
    Citations (28)
    The infrared spectra of the ν5 and ν3 + ν6 bands of CH3I have been measured with a resolution of about 0.03 cm−1. The excited states of these bands form a Fermi diad and, from the analysis of about 600 lines in the spectra, the matrix element of the Fermi-resonance operator was determined. From this the cubic normal-coordinate force constant k356 was found to be 29.40 cm−1. In addition to the Fermi resonance, a further perturbation due to an x-y-type Coriolis resonance between the states | υ5 = 1 〉 and | υ3 = 1, υ6 = 1 〉 was discovered and analyzed.
    Diad
    Fermi resonance
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    Abstract For a molecule affected by Fermi resonance, we establish, up to third order of approximation, the general formulae relating the spectroscopic constants to the mean value of the vibrational energy (in any Fermi polyad) and to the spacings of vibrational energy levels (in a Fermi diad or a Fermi triad).
    Fermi resonance
    Diad
    Triatomic molecule
    Fermi contact interaction
    Linear molecular geometry
    Fermi energy
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    Absorption bands of carbon dioxide involving the Fermi diads 10°0, 02°0 and 10°1, 02°1 have been investigated and molecular constants obtained. The variation in the centrifugal stretching constants which has been observed in the component levels is such that the average centrifugal stretching constant of the diad is very nearly the same as that of the vibrationless ground state of CO2.
    Diad
    Fermi resonance
    Force constant
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    The effect of Fermi resonance on the vibronic energy levels of linear triatomic molecules in Π electronic states has been considered, for states in which both the spin-orbit interaction and the Renner interaction are small compared to the frequency of the bending vibration. The essential difference between the results below and those for Fermi resonance in nondegenerate electronic states is the introduction of two Fermi interaction parameters W1 and W2, rather than one. Specific results are presented for the Fermi diad (100)—(020). The only experimental data available, those for the vibronic states of the A2Π electronic state of BO2, can be nicely fitted with the results of this paper.
    Fermi resonance
    Triatomic molecule
    Diad
    Linear molecular geometry
    Citations (62)