Vibrations in the FIR Region

In this harmonic approximation only transitions appear between these various vibrational energy levels that correspond to a change AM, of a single M, of eq. (4.4) being equal to 1 or -1 (t = X, d or p) while the two other AM, with j A i are equal to 0. IR bands consequently appear at wavenumbers that are related to frequencies of vibrations and related quantities O, by the equation 

Wavenumbers of FIR bands of various isolated H-bonded dimers in the gas phase 

H-bonded dimer Wavenumber (cm ) stretching Wavenumber (cm ) bending Qg and 

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